Aiming at the present situation that forward kinematics of most 6-DOF (degrees of freedom) parallel mechanisms cannot be described with whole analytical solutions, and a very few of them can be described with whole analytical solutions but also with these difficulties, including calculation, programming, and sorting the suitable solution, a general 12-6 Stewart redundant parallel mechanism with hybrid single opened chains was presented, and a whole analytical decoupling algorithm of forward kinematics, which was needed by the closed-loop real-time feedback control system, was constructed. By calculating the position and orientation characteristics set and decomposing the routes of single opened chains, the topological configuration of new mechanism was analyzed, and then the coupling degrees was solved, which were useful to show clearly direction to construct and process the kinematics equations. Based on the topological relations between four coplanar feature points on the moving platform, the combination algorithms of 15 quadratic isomorphic compatible equations were designed, and then the whole analytical solution, which was succinct, symmetric and unique, of forward displacement equations was derived. Based on the method of base points, velocity relations between feature points were established, and then forward velocity equations were solved. Based on compatibility equations and velocity equations, the Jacobian matrix of mechanism was derived, and then three types of singular equations were also derived. Experimental results indicated that the calculated values of forward displacement equations were well consistent with the measured values, and calculation error of forward velocity equations was 0.08%, and the calculation/sampling time ratios of these two equations were 0.21 and 0.32, respectively, which met the real-time demand of control algorithms.