Abstract: A 4-DOF(degree of freedom) parallel positioning platform used in the SEM(scanning electron microscope) is designed.The platform is of simple structure,and easy to integrate micro-operating mechanisms and realize online detection of microstructure's physical performances.The error vector model of the platform is established to realize the high precision positioning platform.Effect of the structure errors and the distribution of upper-stage limbs on the positioning precision of platform's end is analyzed through simulation and emulation.Its output angle displacement in non-DOF directions when operating with biggish load is discussed.