The　research　object　of　this　paper　is　negative　control　system　in　axial　piston　pump,　which　widely　used　in　excavator.　The　control　system　changes　the　delivery　of　the　pump　by　the　complicated　mechanism　to　realize　the　adjustment　of　the　pump　flow　rate.　This　paper　takes　advantages　of　the　AMESim　and　ADAMS　to　build　the　system　hydraulic　model　and　mechanical　model　separately,　and　lets　them　exchange　data　to　complete　the　system　simulation.　Based　on　the　simulation,　we　research　the　effect　of　pilot　spring　and　control　valve　under　lap　on　the　control　system.　©　2012　IEEE.