The　reliability　level　of　CNC　(Computer　Numerical　Control)　grinder　is　usually　assessed　by　fault　data　counted　in　laboratoty　or　in　field,　which　needs　the　grinder　to　be　assembled　and　it　is　one　afterwards　estimation　method　To　evaluate　the　reliability　level　of　CNC　grinder　in　design　phrase,　one　system　reliability　assessment　method　and　algorithm　was　put　forward　by　subsystem＇s　reliability　in　this　article,　which　needs　subsystem　classification,　reliability　test,　distribution　function　fitting,　parameters　estimation　and　reliability　assessment.　The　calculation　result　showed　that　the　method　was　feasible　and　accurate　compared　with　the　traditional　way　The　method　is　one　contribution　to　reliability　design　for　CNC　grinder　and　is　one　reference　to　other　mechatronic　products.