A shape-shifting robot, which named “AMOEBA-I”, has diverse configurations. The accessibility of the robot can be reinforced in the narrow space by changing the configurations. In this paper, a path planning method is presented corresponding to the unique reconfigurable ability of the robot. This method can automatically adjust the computational cost according to the distribution of obstacles in robot's surrounding environment and can automatically select the configuration according to the width of the narrow space. So the robot can reach the target quickly and safely, and the unique accessibility of the shape-shifting robot is fully displayed. The deadlock situation is effectively solved by using the method of the boundary following. It has been validated through simulation results that the robot can change its own configurations to perform the path planning according to the environmental variation. As a result, the length of the path has been reduced effectively.