Abstract: Position analysis of mechanism is to find the straightforward relations between the input and output component, which is elemental task for kinematics analysis and also the basic study of speed, acceleration, stress analysis, error analysis, workspace analysis, dynamic analysis and mechanism synthesis. In practice, solving the forward kinematics means to determine the current, real pose of the end-effectors of the mechanism. According to the reasons above, a new 6-DOF parallel mechanism with 3 limbs is presented. It uses 2-DOF spherical five-bar mechanism as the compound drive device. The length between the three vertexes of the platform is regarded as the restrict condition to obtain the constrained equations and thus the closed-form solution of the forward position problem of the parallel mechanism is studied. The resultant equation is a 16th polynomial. The inverse kinematics’ closed-form solution can be obtained by solving the equations established by the mechanism’s structure feature. At last, a numerical verification is put up to the results of the forward and inverse solutions. The forward solution is very coincident with the inverse solution but only minute error, which is caused by the accumulated com-puting error.

Key words: 6-DOF, Closed-form solution, Forward and inverse solution, Parallel mechanism