According to the problem that the forward displacement of the current six-degree of freedom micro-motion parallel mechanism has no analytical solution or the analytical solution is difficult to solve, a new piezoelectric-drive 12-SPS general parallel mechanism is presented, and the fully decoupled mathematical model of forward kinematics is established. By introducing 12 intermediate variables of 4 feature point coordinates on the moving platform and calculating scales of chains and feature points, 15 quadratic compatible equations are derived. Hereby, the mapping relations between input and output items are obtained. Based on the combination algorithm of isomorphic equations,the forward kinematics equations are converted into 12 linear compatible equations.Based on the matrix singularity, the calculation procedures of intermediate variables under various conditions and 3 kinds of special conditions are discussed, and the final solution is uniquely determined.The experimental result shows that the analytical algorithm has the advantages of high efficiency, high precision,no extraneous root and lost root.