According to the problems of low working efficiency and poor working environment in the actual spherical tank work， a double foot wall climbing robot for spherical tank inwall work is come up. This mechanism used parallel mechanism was constituted of the legs, driven by screw sliding block, which could realize obstacle-surmounting, uniform motion along the wall, turn a corner and so on, and suitable apply to bigger inner diameter spherical tank work. The structural constitution and working principle of parallel wall climbing robot were introduced, implementation of a forward and turning process for wall climbing robot was elaborated, and the kinematics mathematical models were established to obtain its position, velocity and acceleration of inverse kinematics in analytical form. It provides a theoretical tool for the design and control of the mechanism.