The invention relates to a fan frequency control system for a power electronic converter, which is used for performing frequency control on a cooling fan of the power electronic converter. The power electronic converter comprises a power switch tube cooler and a reactor; the cooling fan is a single phase alternating current fan; and the fan frequency control system comprises a temperature detection circuit, a controller and a frequency converter, wherein the temperature detection circuit is used for detecting temperatures of the power switch tube cooler and the reactor and outputting a temperature signal of the power switch tube cooler and a temperature signal of the reactor, the controller is used for generating a frequency instruction according to the temperature signal of the power switch tube cooler and the temperature signal of the reactor, and the frequency converter is connected with the controller and a direct current power supply and is used for performing electric energy transformation on the direct current power supply, and generating an alternating current voltage of the frequency instruction for the single phase alternating current fan so as to adjust the rotating speed of the single phase alternating current fan. The fan frequency control system solves the problem about cooling of the power switch tube cooler and the reactor, and lowers the consumed electricity and noise of the cooling fan to the greatest extent.