Abstract: A new objective function is proposed to satisfy the non-periodic design requirements for solving the dimensional synthesis problem of the rigid-body guidance mechanism of the spatial RCCC. By solving the 21-dimensional spatial RCCC mechanism rigid body guidance synthesis problem in 4 steps, the optimization dimension is effectively reduced. The actual size and installation position parameters of the mechanism can be solved by using formulas. Finally, a practical example is given to prove the effectiveness of the proposed method, thus realizing the solution of the synthesis problem of rigid-body guidance of spatial RCCC mechanism.