The present invention belongs to the optical source measuring technical field, in particular to an LED light flux measuring method. The present invention adopts a reflective cup as an LED light flux collecting device. The concrete operation is that a clamp is used to fix an LED at the bottom of the reflective cup, the luminous direction of the LED points to the big opening of the reflective cup, and a light flux meter is tightly fixed on the big opening of the reflective cup to receive the light signal. Constant current power is used to drive the LED, then the total light flux emitted by the LED is collected and measured by the light flux meter after being gathered by the reflective cup, and finally the numerical reading of the total light flux value is given. The method of the present invention is simple, and the accuracy rate of measuring is high.