One　of　the　most　important　keys　to　consistent　spindle　operation　is　reliability　in　the　manufacturing　and　processing　computer　numerical　control　machine　tools　(CNC).　The　diffusion　kernel　density　estimation　method　is　presented　for　modeling　the　cutting　force　spectrum　and　program　load　of　computer　numerical　control　machine　tools.　The　cutting　experiments　of　the　machining　center　are　conducted　under　multiple　manufacturing　conditions.　The　probability　density　function　and　cumulative　distribution　function　are　derived　from　the　method　proposed　in　this　paper　and　other　traditional　methods.　In　addition,　the　established　method　for　parameter　estimation　is　validated　against　the　coefficient　method　(R2),　root　mean　square　error　(RMSE),　and　K-S　test　methods.　The　proposed　method　establishes　the　distribution　function　and　two-dimensional(2D)　load　spectrum　of　cutting　force　when　CNC　machine　tools　are　used　in　various　machining　conditions.　Finally,　according　to　the　characteristic　analysis　of　the　2D　cutting　force　spectrum,　the　program　load　spectrum　compilation　for　the　CNC　spindle　is　completed　under　multiple　manufacturing　conditions.