According to the parallel mechanism design theory and systematical method based on position and orientation characteristic (POC), a total topological structures analysis was performed on seven typical new SCARA parallel mechanisms (PMs) with proposed practical value. Five major topological features were revealed, which were POC set, degree of freedom (including the selection of drive pair), over-constraint degree, coupling degree and input-output motion decoupling relationship of PMs. It was found that the coupling degree of these PMs were bigger with κ=2, which meant that the forward kinematics solutions and inverse dynamic solution of the PMs were very complete. Therefore, decoupling and optimization of these PMs were completed based on the proposed mechanism topological structural decoupling principles, and 14 new equivalent mechanisms with lower coupling degree which had the same POC and DOF were achieved. Thus the 4-DOF mechanism with three translations and one rotation which can achieve Schonflies motion can be enriched greatly, and the forward kinematics solutions and inverse dynamic solution of these PMs can be obtained easily, and the numerical solution can be gotten conveniently by using one dimensional searching method. The research provided a theoretical basis for the kinematics synthesis and analysis, design and applications for these new SCARA PMs.