Abstract: An approach combining numerical analysis with optimization for the workspace analysis of the parallel manipulator 6 - SPS is proposed. According to the features of the parallel manipulator and the practical requirements, the totality of points that can be reached by the centre of the upper platform are classified as lying either within the reachable space with a given attitude of the upper platform, or within the workspace. By means of a procedure starting from the highest or the lowest point, these working envelopes with known structural parameters can be calculated readily. The relations between the working envelope and the structural parameters are discussed. Some regular variations have been found. These results obtained can serve as a means of sizing the practical parameters.