Abstract: To deal with the problem of the manufacturing precision reliability decline due to the mechanical parts' wear and deformation with increasing service time, the soft compensation for the machine tool geometric errors is put forward to maintain the manufacturing precision reliability of the CNC camshaft grinder.The geometric error source is analyzed, the precise grinding kinematics equations that the errors are embodied are deduced by the multi-body kinematics, and the iteration solving manner is introduced.The geometric errors of one camshaft grinder are compensated and simulated and the manufacturing experiments are implemented.The maximum contour errors of cams manufactured by the non-compensated, compensated and new CNC camshaft grinder are tested by the Wilcoxon rank-sum test.Results show that the soft error compensation plays notable effect in maintaining the camshaft grinder's manufacturing precision reliability.It puts forward one manner to manufacture high precision products for the low precision camshaft grinder by the research results and widens train of thought for studying machine tools reliability.