An algorithm using iterative path search technique to outline the boundary profile of a parallel manipulator with spheical points to connect thde platform and all branch kinematic chains. Geometrical constrains between branch kinematic chains and platform are analysed on the basis of subworkspace division of branch chains so as to obtain the restrictive of subworkspaces.Moving the platform from a point inside the workspace to outside the boundary along a line, adjusting the orientation of the platform and regulating the step length under a restrictive condition, the boundary of workspace could be obtained when the step length is very small. Compared with the conventional algorithm of optimum path search, the evaluation presented in this paper is faster in caculation and simpler in porgram. Having the benifit of controling the orientation of platform in search process, this evaluation is of some help to study the dexterity of parallel manipulator. An example of the Stewart manipulator is given in this paper.