The invention relates to a tool for replacing an engine rocker arm. The tool comprises a support structure and a rocker arm pressing tool arranged on the support structure; the support structure comprises a support beam and fixing clamps, wherein the fixing clamps are arranged at the two ends of the support beam and used for clamping an engine cylinder body; and the rocker arm pressing tool comprises a driving structure arranged on the support beam in a sliding mode and a pushing rod structure connected to the driving structure, wherein the pushing rod structure corresponds to valve seat ringsor valve pressing blocks. According to the tool for replacing the engine rocker arm, when a valve rocker arm is replaced, time and labor are saved, and damage and loss of other parts are avoided.