Based　the　principle　of　online　dynamic　balance　device　with　balancing　disks,　the　design　method　of　embedded　double-face　online　dynamic　device　was　proposed.　Balancing　disks　could　be　disengaged　from　the　spindle　by　Hydraulic　system,　and　the　rotating　speed　of　the　disengaged　disk　was　kept　steady　and　under　the　speed　of　the　spindle　by　friction　torque.　The　systems　of　signal　acquisition,　signal　analysis　and　control,　hydraulic　pressure　were　designed.　The　feasibility　was　proved　and　analyzed　by　examples.