Aiming at eliminating the disadvantage in current post-processing system which cannot generate the CNC instruction for serial-parallel machine tool, post-processing algorithm, fit for this sort of processing device, was discussed based on XYZ-3RPS serial-parallel machine tool model. By the analysis of structure and post-processing process of the serial-parallel machine tool, the key algorithm of post-processing which includes interpolation algorithm for cutter bit data under Cartesian coordinates, the inverse solution under coordinate of machine tool and the interference checking algorithm were proposed. Meanwhile, some unqualified cutter bit positions were corrected and cutter location data files had been changed into machine tool driver files. Finally, the validity of the algorithm was verified by the processing experiments of vane and sphere.