The invention relates to a rotor excitation method and device of a synchronous motor. According to the method, electric energy of a DC/AC power supply is transmitted to a rotor excitation winding in a non-contact mode by employing a resonant wireless electric energy transmission mode, so that rotor electrical excitation or hybrid electrical excitation is achieved. The device comprises an emission end and a receiving end, wherein the emission end is fixedly combined with an engine base, the receiving end synchronously rotates with a rotor and is connected with the rotor excitation winding, the emission end comprises a resonant excitation circuit, an emission end compensation circuit and an emission coil which are connected, the receiving end comprises a receiving coil, a receiving end compensation circuit and rectification conversion circuit which are connected, the rectification conversion circuit is connected with the rotor excitation winding, and the resonant excitation circuit comprises a power input interface and is used for inputting the electric energy from the power supply and continuing to simulate the emission coil and the emission end compensation circuit to work in a resonant state. Compared with the prior art, the device has the advantage of a reliable structure, wireless excitation can be achieved, and an excitation current can be adjusted to satisfy the running demand of the motor under various working conditions.