The　key　to　improve　the　properties　and　intelligent　controlling　level　of　a　machine　is　to　optimize　the　mechanical　properties　of　the　major　mechanisms,　while　the　core　problems　are　how　to　evaluate　the　mechanical　properties　reasonably　and　how　to　control　the　machine　fine.　Due　to　the　complexity　and　diversity,　the　single　performance　indexes　of　closed-chain　mechanism　were　analyzed　based　on　principal　component　analysis　(PCA)　method.　Then　the　comprehensive　performance　evaluation　index　of　the　mechanism　was　integrated.　A　comprehensive　performance　index　of　crank-rocker　mechanism　which　was　a　kind　of　typical　closed-chain　mechanism　was　proposed,　and　evaluation　method　was　studied.　And　scientific　research　basis　for　the　mechanism　synthesis　and　optimum　order　was　provided　by　the　principal　component　score.