The invention discloses a virtual signal injection-based maximum torque current ratio control method of a synchronous motor. A tidy signal is injected to a stator current angle to obtain a derivativeof an electromagnetic torque on the stator current angle, and then a stator current angle reference value is obtained; and next, a stator current amplitude reference value is obtained by a fixed torque constant and an open loop compensation integrator, and then a d-q-axis current reference value is obtained. By virtue of the more accurate formula disclosed in the invention, the steady state precision is ensured; and by virtue of square wave injection and processing method, dynamic response is improved.