The invention relates to an optical transmissivity testing device based on light source electrical modulation, which belongs to the technical field of optical test. The prior testing device uses a mechanical chopper to modulate test light, obtained alternating light is not exact square wave, and electrical signals sent by a photoelectric detector are not exact square wave signals, so that the test precision is low. In addition, the mechanical chopper is a large precision machinery part, has large size and high price and results in the large size and the high price of the testing device directly. The invention has a structure as follows: a light source and a power supply form a loop; the light source, a collimating lens and a collector lens are coaxial optically; an integrating sphere light inlet is arranged on the focus of the collector lens; the photoelectric detector is arranged at the position, away from the light inlet, of an integrating sphere body; the photoelectric detector is connected with a microprocessor; a pulse modulation signal output end of a signal generator is connected with a controllable switch tube; a pulse control signal output end is connected with the microprocessor; and the controllable switch tube is arranged on the loop formed by the light source and the power supply. The optical transmissivity testing device based on the light source electrical modulation is applied to the optical transmissivity test of optical elements.