The invention discloses a method of solving a transient power angle of a synchronous generator, including the following steps: S1, voltage and current transient data under a grid disturbance are acquired from a synchronous generator port, the voltage and current transient data are expressed to transient signal sine expression, the instantaneous phase angles of the voltage and the current are calculated, and the instantaneous phase angle difference between the voltage and the current is calculated; S2, subtraction between the calculated a phase current instantaneous phase angle and an a-phase current steady-state phase angle before grid disturbance is carried out, an a-phase current phase angle change value is obtained, the transient included angle between a rotor d axis and a stator a phase magnetic flux axis can be calculated by the current phase angle change value, and based on the calculated transient included angle between the rotor d axis and the stator a phase magnetic flux axisand the instantaneous phase angle difference between the voltage and the current, the transient power angle of the synchronous generator is calculated.