A control circuit of a switching power supply having a high-voltage side switching element and a low-voltage side switching element connected in series between a positive potential end and a ground of a direct current power supply, the control circuit comprising: a central control circuit which has a first control port, a second control port, and a third control port, wherein the first control port and the second control port are respectively configured to output a control signal of turning on and off the high-voltage side switching element and the low-voltage side switching element; and a current selection circuit which is disposed between the third control port and the ground and has two or more selection terminals (X1,..., XN), a connection state between the selection terminals (X1,..., XN) being switched between different connection states to adjust the output current value of the switching power supply, wherein the selection terminals (X1,..., XN) can be switched between the different connection states to adjust a switching frequency of the switching power supply during work and wherein the switching frequency further controls the output current value of the switching power supply, wherein the different connection states include disconnection, shorting, and connection with a resistor having a predetermined resistance value, wherein the current selection circuit further includes: at least one current selection subunit, and each current selection subunit is connected to the corresponding selection terminal (X1,..., XN), characterized in that each current selection subunit includes at least two current selection branches connected in parallel, and each current selection branch includes a resistor (R55, R41, R54, R40) and a switching element (Q21-Q24) connected in series between the third control port and the ground, wherein trigger voltages required to turn on the switching element (Q21-Q24) of each branch of the at least two current selection branches are made different from each other, and each switching element (Q21-Q24) has a control end configured to control the on or off of the switching element (Q21-Q24), and the control end is connected to the 5 corresponding selection terminal (X1,..., XN) through a resistor (R42, R45) and/or a diode (Z23, Z24), wherein further a switching element (Q21, Q22) where the control end is connected to a diode (Z23, Z24) needs a higher trigger voltage to be turned on. a central control circuit which has a first control port, a second control port, and a third control port, wherein the first control port and the second control port are respectively configured to output a control signal of turning on and off the high-voltage side switching element and the low-voltage side switching element; and a current selection circuit which is disposed between the third control port and the ground and has two or more selection terminals (X1,..., XN), a connection state between the selection terminals (X1,..., XN) being switched between different connection states to adjust the output current value of the switching power supply, wherein the selection terminals (X1,..., XN) can be switched between the different connection states to adjust a switching frequency of the switching power supply during work and wherein the switching frequency further controls the output current value of the switching power supply, wherein the different connection states include disconnection, shorting, and connection with a resistor having a predetermined resistance value, wherein the current selection circuit further includes: at least one current selection subunit, and each current selection subunit is connected to the corresponding selection terminal (X1,..., XN), characterized in that each current selection subunit includes at least two current selection branches connected in parallel, and each current selection branch includes a resistor (R55, R41, R54, R40) and a switching element (Q21-Q24) connected in series between the third control port and the ground, wherein trigger voltages required to turn on the switching element (Q21-Q24) of each branch of the at least two current selection branches are made different from each other, and each switching element (Q21-Q24) has a control end configured to control the on or off of the switching element (Q21-Q24), and the control end is connected to the 5 corresponding selection terminal (X1,..., XN) through a resistor (R42, R45) and/or a diode (Z23, Z24), wherein further a switching element (Q21, Q22) where the control end is connected to a diode (Z23, Z24) needs a higher trigger voltage to be turned on. at least one current selection subunit, and each current selection subunit is connected to the corresponding selection terminal (X1,..., XN), characterized in that each current selection subunit includes at least two current selection branches connected in parallel, and each current selection branch includes a resistor (R55, R41, R54, R40) and a switching element (Q21-Q24) connected in series between the third control port and the ground, wherein trigger voltages required to turn on the switching element (Q21-Q24) of each branch of the at least two current selection branches are made different from each other, and each switching element (Q21-Q24) has a control end configured to control the on or off of the switching element (Q21-Q24), and the control end is connected to the 5 corresponding selection terminal (X1,..., XN) through a resistor (R42, R45) and/or a diode (Z23, Z24), wherein further a switching element (Q21, Q22) where the control end is connected to a diode (Z23, Z24) needs a higher trigger voltage to be turned on.