This　research　uses　prings　to　imitate　humanoid　lumbar　spine　of　a　robot,　and　analyzes　the　problem　of　lumbar　spine　of　flexibility　of　the　botot.　A　simplified　model　is　obtained,　which　is　linearized　and　its　equations　of　state　are　established.　The　simplified　dynamic　model　is　obtained　by　design　and　its　structure　is　simple,　and　controlling　of　the　model　is　easy　and　effective.　Validity　of　the　system　modeling　is　proved　through　the　mathematics＇　method.