The invention discloses a circuit system capable of reducing a power at fixed time and automatically reducing the power at over-temperature for an LED power supply. The circuit system comprises an LEDthree-in-one dimming voltage division integral circuit, a fixed-time power reduction setting circuit, an over-temperature detection sampling circuit, a power supply voltage stabilization reference circuit, an MCU microcontrol circuit, a PWM photoelectric isolation control circuit and a master control IC output current adjustment control circuit, wherein the MCU microcontrol circuit is connected with the LED three-in-one dimming voltage division integral circuit, the fixed-time power reduction setting circuit, the over-temperature detection sampling circuit, the power supply voltage stabilization reference circuit, the MCU microcontrol circuit and the PWM photoelectric isolation control circuit, and the master control IC output current adjustment control circuit is connected with the PWM photoelectric isolation control circuit, By the circuit system, fixed-time power reduction of the LED power supply can be achieved, and automatic power generation after over-temperature can be achieved.