The present invention discloses a varifocal laser processing system and method based on a variable light spot diffractive element. The system includes a laser device for generating a laser, a collimating lens for changing a light path and a diffractive optical element module for controlling light spot focal point distribution. The laser emitted by the laser device passes through the collimating lens to irradiate the diffractive optical element module, and the laser focused by the diffractive optical element module irradiates a to-be-processed workpiece; and the diffractive optical element module includes at least two DOE lenses oppositely distributed in an axial direction and a rotary actuator driving the DOE lenses to rotate. The rotary actuator drives at least one DOE lens to rotate with a central axis as a rotating center, thereby changing a position of a focal point generated after the laser is focused by the diffractive optical element module.