An offset voltage eliminating circuit structure for a protection mechanism of a dimmer, comprising: a constant current source including an output (Pout) for outputting a stable current, the output (Pout) connected with a dimming signal input (ADJ_in) through a current-limiting resistor, the dimming signal input (ADJ_in) connected with an output of an external dimmer; a subtractor formed by a third operational amplifier and second, third, fourth and fifth resistors (R2, R3, R4, R5), the second and the third resistors (R2, R3) connected in series, and the non-inverting input of the third operational amplifier connected between the second and the third resistors (R2,R3),, the fourth and the fifth resistors (R4, R5) connected in series, and the inverting input of the third operational amplifier connected between the fourth and the fifth resistors (R4, R5), characterized in that the second, third, fourth and fifth resistors (R2, R3, R4, R5) have the same resistances; and the other end of the second resistor is connected with the output (Pout), and the other end of the third resistor is connected to ground; and the other end of the fourth resistor is connected between the output of the third operational amplifier and the inverting input of the third operational amplifier, and the other end of the fifth resistor being input with an offset reference voltage (Voffset); and the offset voltage eliminating circuit structure for the protection mechanism of the dimmer further comprising a hysteresis comparator including a non-inverting input, an inverting input and an output capable of outputting a GD pulse signal, the non-inverting input connected to the output of the third operational amplifier, and the inverting input being input with a saw-tooth wave. a constant current source including an output (Pout) for outputting a stable current, the output (Pout) connected with a dimming signal input (ADJ_in) through a current-limiting resistor, the dimming signal input (ADJ_in) connected with an output of an external dimmer; a subtractor formed by a third operational amplifier and second, third, fourth and fifth resistors (R2, R3, R4, R5), the second and the third resistors (R2, R3) connected in series, and the non-inverting input of the third operational amplifier connected between the second and the third resistors (R2,R3),, the fourth and the fifth resistors (R4, R5) connected in series, and the inverting input of the third operational amplifier connected between the fourth and the fifth resistors (R4, R5), characterized in that the second, third, fourth and fifth resistors (R2, R3, R4, R5) have the same resistances; and the other end of the second resistor is connected with the output (Pout), and the other end of the third resistor is connected to ground; and the other end of the fourth resistor is connected between the output of the third operational amplifier and the inverting input of the third operational amplifier, and the other end of the fifth resistor being input with an offset reference voltage (Voffset); and the offset voltage eliminating circuit structure for the protection mechanism of the dimmer further comprising a hysteresis comparator including a non-inverting input, an inverting input and an output capable of outputting a GD pulse signal, the non-inverting input connected to the output of the third operational amplifier, and the inverting input being input with a saw-tooth wave.