The invention discloses an active imaging method and system based on synchronous triggering of an LED and a camera. A digital processor emits a path of control signals to control the LED to emit light pulses, the light pulses are reflected by a target object, pass through an imaging cameral lens and then are received by the external triggering camera, the step is repeated from two times to a hundred million times, and then an image of the target object is output. First path output of the digital processor is connected with the LED, second path output of the digital processor is connected with the external triggering camera, and light pulse signals of the LED are reflected by the target object, pass through the imaging cameral lens and then are received by the external triggering camera. The LED and the external triggering camera which are low in cost are adopted, so that overall cost is low; by the adoption of a gating mode, the influence of back scattering light and stray light can be effectively eliminated, interference in active imaging by the working environment and kinds of severe weather such as fog, haze, rain, snow, smoke and stray light is reduced, and the active imaging method and system have the advantages of being low in cost and high in adaptability.