The invention discloses an on-off control method for a dual-power triple-CPU projector, which includes a standby CPU, a standby power supply, a system main CPU, a system main power supply and also includes a signal processing CPU; the signal processing CPU is used for realizing automatic starting function; the GPIO port of the signal processing CPU is connected with an infrared remote control receiver module for simulating a starting remote control instruction and sending the starting instruction to the remote control receiver module, the signal processing CPU continuously detects the synchronization field line of the input signal, if an input signal is detected, the system automatic starting function is executed, namely the signal processing CPU simulates the remote control starting instruction and sends the starting instruction to the standby CPU through the GPIO port, and the standby CPU starts the system main power supply. The invention also proposes a mode that the projector adopts the signal processing CPU to detect if synchronization field line of the input signal exists under standby state, and determines whether starting the projector according to if the input signal exists, and accordingly improves the intelligent degree of the projector.