With a mobile manipulator as the research object, a path planning method of mobile manipulator based on the representation space is proposed in this paper. The state space model of the mobile manipulator is defined and constructed in this method. According to internal mechanism and external environment constraints, the achievable stretch of system state is described. On this basis, A∗algorithm is adopted to carry out the path planning search, analyzing spatial variable trends on each dimension of the representation space, and setting up the function parameters for A∗algorithm so that the motion trajectory will be more reasonable. The effectiveness of the proposed method is verified by simulation experiments.