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.