The　spindle　system　is　the　key　component　of　the　CNC　(computer　numerical　control)　grinding　machine.　In　order　to　explore　the　factors　affecting　the　reliability　of　the　CNC　grinding　machine　spindle　system　and　find　out　measures　to　improve　the　reliability　of　the　CNC　grinding　machine,　this　paper　proposed　a　reliability　evaluation　algorithm　based　on　fault　data.　Five　common　distribution　functions　are　used　to　establish　the　mathematical　model　of　the　time　between　failures.　After　parameter　estimation,　fitting　test,　and　optimal　model　selection,　the　distribution　model　of　the　spindle　system　is　finally　determined.　Monte　Carlo　method　is　used　to　verify　the　accuracy　of　the　distribution　model,　and　the　mean　time　between　failures　(MTBF)　of　the　spindle　system　is　calculated.　At　the　same　time,　according　to　the　fault　data,　the　failure　mode　effects　and　criticality　analysis　(FMECA)　and　fault　tree　analysis　(FTA)　are　used　to　find　out　the　key　fault　factors,　and　the　corresponding　improvement　measures　are　put　forward.　Finally,　the　characteristics　and　application　of　the　five　distribution　models　are　discussed.　The　above　analysis　methods　have　been　effectively　applied　in　the　project　and　are　one　reference　for　the　reliability　evaluation　and　redesign　of　other　electromechanical　products.