The method includes: receiving an encoder signal and a ray machine output beam signal, and initially synchronizing the encoder signal and the ray machine output beam signal; recording coded value M of the encoder at moment tm, and coded value N of the encoder at moment tm+1, where M, N, and m are integers; determining that duration from the moment tm to the moment tm+1 is an actual output beam time interval T of the ray machine, when it is determined that a difference value between the coded value M and the coded value N satisfies preset value a, a being an integer; determining gap time TG in the actual output beam time interval T based on a preset output beam time interval TJ of the imaging system and the actual output beam time interval T; and controlling the ray machine not to emit beam within the gap time TG.