The invention relates to a multi-stage electric cylinder for a robot. A fixing sleeve serves as a static end in the working process and is installed on a carrier, a driving shaft is located in a hollow screw, the lower end of the driving shaft penetrates out of the fixing sleeve, a rotary motion pair is formed between the lower end of the driving shaft and the fixing sleeve, the upper end of the driving shaft is rotationally connected with the inner wall of the hollow screw, and the middle section of the driving shaft and the lower end of the hollow screw form a spiral motion pair. Multiple stages of sequentially nested telescopic rods are arranged between the hollow screw and the fixing sleeve, the inner wall of the lower end of the first-stage telescopic rod and the hollow screw form a spiral motion pair, linear motion pairs are formed between all stage of telescopic rods and between the last stage of telescopic rod and the fixing sleeve, and the outer wall of the lower end of each stage of telescopic rod is provided with an outer lower mechanical limiting device which drives the next stage of telescopic rod to do linear extension motion. A power source drives the driving shaft to rotate forwards and reversely, so that all stages of telescopic rods are driven to stretch or retract in sequence. The multi-stage electric cylinder achieves the design purpose of miniaturization while achieves a large expansion ratio, single driving and cleanness.