The invention discloses a power control method for a stationary frequency converter. When the stationary frequency converter works in a weak magnetic region, an auxiliary control ring which takes the cosine value of a network bridge triggering angle as a control target is introduced, and the cosine value is outputted and added to a machine-end voltage reference value, thereby achieving the optimization power control of machine-network coordination of the stationary frequency converter. When a stationary frequency converter system enters into a weak magnetic working region, the auxiliary control ring is started and the closed-loop PI control of the cosine value UK of the network bridge triggering angle is controlled, wherein the reference value can be set. The beneficial effects of the invention are that the method reduces the demands for a DC loop current under the condition of meeting the condition of system output power, and gives consideration to the impact from the amplitude fluctuation of a medium voltage power supply; the method is convenient to implement through software, and facilitates engineering debugging.