The present invention discloses a standing wave linear accelerator, comprising: a microwave device configured to generate microwave; an electron beam emitting device configured to emit electron beam; an accelerating device configured to receive the microwave generated by the microwave device and form a microwave electric field, to accelerate electron beams generated from the electron beam emitting device and undertake the accelerated electron beam targeting to emit X ray beam; a synchronous device generating synchronous pulse signal; and a quick beam emitting device receiving the synchronous pulse signal generated by the synchronous device, wherein the microwave device runs and generates microwave in advance before the operation of the electron beam emitting device based on the synchronous pulse signal, and the quick beam emitting device drives the electron beam emitting device to emit electron beam after power of the microwave generated by the microwave device reaches stable state, so that the accelerating device emits X ray beam. In the accelerator, the microwave system and the electron beam emitting device do not work at the same time, and the accelerator electron beam emitting system is started only when the AFC is put into operation and runs stably.