The invention provides a method for measuring movement velocity of a high-density plasma and an optical system. On the basis of a principle of light refraction occurrence at a high-density-gradient plasma boundary, an optical system is designed to generate two light beams with incidence at small angles, wherein the directions of the two light beams are perpendicular to the movement direction of the plasma boundary; and a 4f system is used for imaging and separation of the two light beams: a first light beam and a delay beam is realized at a focal point of a first lens. When velocity measurement is carried out, some light of the first light beam is deflected at the boundary of the plasma in high-speed movement and the deflected light enters the optical system where the delay beam is located; an image of the boundary of the plasma at a corresponding time is displayed at a camera; after time delay of the delay beam, the shape and location of the plasma at the corresponding time are displayed at the camera; and average movement velocity information of the plasma boundary at a corresponding time interval can be obtained in a shadow image. With a laser shadow system, the velocity of the boundary of the plasma in high-speed movement can be obtained effectively; and the result is reasonable and accurate.