The crawler-type maintenance robot designed for the steam generator in nuclear power plants faces challenges such as inadequate adaptability and low maintenance efficiency. In order to address the task of maintaining multiple specifications of heat transfer tubes in the steam generator, a novel quadruped crawling maintenance robot with a new mechanism was proposed and gait planning was conducted. Firstly, the configuration and overall design of the robot were determined based on the requirements to adapt to multiple specifications of tube plates, and the main motion mode of the crawling robot was identified, along with providing the workspace for tools. Subsequently, research on gait planning was conducted for different types of tube plates, including planning linear motion gaits and turning motion gaits on tube plates arranged in triangular and square patterns. Finally, the motion simulation experiments of the robot were conducted through a joint simulation of V-REP and Python. The results demonstrate that the crawling robot can execute linear and turning motions on tube plates of various specifications, showcasing the rationality of the mechanism and the feasibility of the motion.