A　dynamic　model　of　low-voltage　molded　case　circuit　breaker　operating　mechanisms　was　built　based　on　multi-body　dynamics　adopting　virtual　prototyping　technology.　An　experiment　was　done　to　verify　the　model.　The　results　showed　that　the　simulation　is　in　good　agreement　with　the　test　results　of　the　real　circuit　breaker.　It　is　significant　that　the　model　can　be　used　to　study　the　interrupting　characteristics　of　low-voltage　circuit　breaker　and　provide　a　good　basis　for　circuit　breaker　optimum　design.　Considering　the　electro-dynamic　repulsion　force　effect,　the　time　of　the　interrupting　process　was　shortened　about　2　ms.　It　is　indicated　that　the　centroid　y　coordinates　and　mass　of　upper　linkage　have　the　most　influence　on　angular　velocity　of　moving　contact　and　the　centroid　position　and　mass　of　trip　are　next　to　them.　After　optimization　design,　the　average　angular　velocity　of　moving　contact　is　raised　13.3%.