The invention discloses a linear-rotary combined motion device for an electrolytic machining machine tool main shaft, and belongs to the field of machine tool spindles. According to the composite motion device, an input shaft and the main shaft are coaxially and rotationally installed in a box body, one end of the input shaft is provided with a piston cylinder, one end of the main shaft is provided with a piston coordinated with the piston cylinder, two small oil cylinders are arranged on the side wall of the cylinder body of the piston cylinder, the cam profile of each upper cam and the cam profile of each lower cam abut against a small oil cylinder piston rod of the corresponding small oil cylinder; and the input shaft is ingeniously connected with the main shaft through a piston cylinder structure, meanwhile, a cam structure is used for realizing the change of the space of hydraulic oil in the piston cylinder, so that the vertical reciprocating rectilinear motion of the main shaft is realized, the main shaft rotates along with the input shaft, the main shaft can be driven to rotate and linearly move by only one driving motor, the linear motion amplitude can be controlled by thecam track, the structure is simple and ingenious, the control is simple, flexible and convenient, and the movement requirement of the electrolytic machining machine tool main shaft is greatly met.