A method for checking an out-of-step of a synchronous motor, comprising: detecting three-phase currents of the synchronous motor (101, 401); determining whether a relationship between the three-phase currents satisfies a preset requirement (102, 402); if no, determining that the synchronous motor is out of step, the method further comprising: determining a type of the out-of-step of the synchronous motor according to the relationship between the three-phase currents, in which the type of the out-of-step of the synchronous motor comprises a first type of out-of-step and a second type of out-of-step, wherein determining a type of the out-of-step of the synchronous motor according to the relationship between the three-phase currents comprises: determining whether each current of the three-phase currents is a direct current; if yes, determining that the type of the out-of-step of the synchronous motor is the first type of out-of-step; if no, calculating a maximum value of each current of the three-phase currents to obtain three maximum values; determining whether a ratio between a maximum value of the three maximum values and a minimum value of the three maximum values is larger than or equal to a preset threshold; and if yes, determining that the type of the out-of-step of the synchronous motor is the second type of out-of-step. detecting three-phase currents of the synchronous motor (101, 401); determining whether a relationship between the three-phase currents satisfies a preset requirement (102, 402); if no, determining that the synchronous motor is out of step, the method further comprising: determining a type of the out-of-step of the synchronous motor according to the relationship between the three-phase currents, in which the type of the out-of-step of the synchronous motor comprises a first type of out-of-step and a second type of out-of-step, wherein determining a type of the out-of-step of the synchronous motor according to the relationship between the three-phase currents comprises: determining whether each current of the three-phase currents is a direct current; if yes, determining that the type of the out-of-step of the synchronous motor is the first type of out-of-step; if no, calculating a maximum value of each current of the three-phase currents to obtain three maximum values; determining whether a ratio between a maximum value of the three maximum values and a minimum value of the three maximum values is larger than or equal to a preset threshold; and if yes, determining that the type of the out-of-step of the synchronous motor is the second type of out-of-step. determining whether each current of the three-phase currents is a direct current; if yes, determining that the type of the out-of-step of the synchronous motor is the first type of out-of-step; if no, calculating a maximum value of each current of the three-phase currents to obtain three maximum values; determining whether a ratio between a maximum value of the three maximum values and a minimum value of the three maximum values is larger than or equal to a preset threshold; and if yes, determining that the type of the out-of-step of the synchronous motor is the second type of out-of-step.