The invention discloses a slipping device for a petroleum drilling machine. The device comprises a slipping oil cylinder and a slipping rack, edge beams are arranged at the front and rear ends of theslipping rack respectively, and guide blocks are arranged at the left and right ends of each edge beam respectively; a self-locking beam is arranged in the middle of the slipping rack, the self-locking beam is parallel to the two edge beams, and a connection lug plate is vertically arranged on the upper portions of the self-locking beam and the two edge beams; a set of locking mechanisms are symmetrically arranged on the self-locking beam along the two edges of the connection lug plate respectively, and the locking mechanisms are connected with a hydraulic power and control box; an oil inlet port and an oil returning port of the slipping oil cylinder are connected with the hydraulic power and control box separately; a first double lug plate is arranged at the bottom end of a cylinder bodyof the slipping oil cylinder, the first double lug plate is hinged to a connection component through a hinge pin, and the connection component is connected with a drilling machine traction base; a second double lug plate is arranged at the end of a piston rod of the slipping oil cylinder, and the second double lug plate is hinged to the connection lug plate on the slipping rack through a second hinge pin. The welded low-gravity-center rack is adopted for the slipping device, remote control is achieved, and the device is high in reliability.