The invention relates to an application device based on light intensity transmission equation phase retrieval. According to the device, a light splitting sheet, a reflector and a spatial light modulator are used for dividing an imaging light beam into three sub-light beams; and an angular spectrum transfer function of the spatial light modulator is adjusted to make CCD obtain a focusing intensity image and a positive defocusing intensity image and a negative defocusing intensity image at the same time, wherein the positive defocusing intensity image and the negative defocusing intensity image have identical defocusing distance; then the light intensity transmission equation phase retrieval technology is applied on the collected images to rebuild the phase of an object. No mechanical movement or adjustment is required during the collecting process and only single exposure of single camera is needed so that quantitative phase position images can be retrieved stably and fast by use of the system; the application of traditional light intensity transmission phase imaging can be expanded to measure objects moving at high relative speed.