The invention discloses a mould locking device for an electric injection molding machine, which comprises a front moulding plate, a middle moulding plate and a back moulding plate which are arranged sequentially from front to back in parallel, wherein four pull rods are arranged between the front moulding plate and the back moulding plate, and the front ends of the pull rods are fixedly connectedwith the front moulding plate. The tail ends of the pull rods are connected with a mould locking piston, and an outer ring of the mould locking piston is glidingly matched with a mould locking oil cylinder which is fixedly connected with the back moulding plate. The back moulding plate is matched with at least one set of hydraulic jacks, and controls the movement of the mould locking piston. A mould moving motor which is matched on the back moulding plate is connected with a mould moving roll ball screw rod which is positioned in the center of the back moulding plate by driving. The front endof the mould moving roll ball screw rod is fixedly connected with the back end of the middle moulding plate through a main shaft, wherein the back end of the middle moulding plate adopts a horn-shaped structure, and the middle stressing and force transferring effect is uniform. The back moulding plate is provided with a mould adjusting component, a mould locking component and a quick mould movingcomponent integrally, and the structure is compact. The mould moving roll ball screw rod and the main shaft adopt a thread pitch multi-head roll ball screw rod structure, and the mould moving speed is high.