Provided is a ceaseless grease injection grease gun. A grease injection cylinder body is installed at the upper portion of a grease storage cylinder. A grease injection pipe is installed on the grease injection cylinder body. A grease push piston is arranged in the grease storage cylinder and supported by a spring. A gun cylinder seal ring is arranged in an annular groove in the grease push piston. A left inlet grease discharge cavity, a right inlet grease discharge cavity and a valve ball cavity are formed in the grease injection cylinder body. A left piston is placed in the left inlet grease discharge cavity. A right piston is placed in the right inlet grease discharge cavity. A left valve port and a right valve port are formed in the grease injection cylinder body. A switch valve ball is placed in the valve ball cavity. The left piston and the right piston are connected together through a linkage plate so that linkage can be achieved. A left grease inlet hole and a right grease inlet hole are formed in the lower portion of the grease injection cylinder body. The grease storage cavity is communicated with the left inlet grease discharge cavity through the left grease inlet hole. The grease storage cavity is communicated with the right inlet grease discharge cavity through the right grease inlet hole. A supporting plate is arranged on the outer side of the grease injection cylinder body. A lever type handle is connected with the right piston through a piston pin shaft in a hinged mode and connected with the supporting plate through a supporting pin shaft in a hinged mode. Bidirectional ceaseless grease injection can be achieved, and work efficiency can be improved.