A dynamic phase acquisition device includes a light collecting opening, a semi-reflecting and semi-transmitting mirror, a phase shifter, a polarizer, a plane reflector, a photosensing element and a phase processor. In the dynamic phase acquisition device, light passes through the light collecting opening to the semi-reflecting and semi-transmitting mirror, and then is divided into two channels. One channel of the light sequentially passes through the phase shifter, the polarizer to the photosensing element, to form a first image; the other channel of the light, after being reflected by the plane reflector, directly passes through the polarizer to the photosensing element, to form a second image. The photosensing element sends the first image and the second image to the phase processor, and the phase processor obtains phase data; and a leading or lagging phase shift range of the phase shifter is 1 degree to 20 degrees. By using the phase shifter to provide a lead or a lag of a small amount of degrees, such as from 1 to 20 degrees, or even from 5 to 10 degrees, phase data can be obtained via two-path image detection, thus eliminating the need for optical elements for at least one path detection, and thereby simplifying the structure and reducing costs.