The shape of the belt is always decided by the different meshing conditions of flexible synchronous belt and pulley in complete and incomplete meshing zone.According to the characteristic of double helical tooth synchronous belt,the mesh form of the double helical tooth synchronous belt and pulley at different meshing zone is studied.By using the dimensional differential geometry,the digital design space geometry model of the tooth of synchronous belt is built,and for this digital modeling mechanism,the 3D solid model design is carried out,the precision model supports for the mould digital design and dynamics analysis of synchronous belt drive system are provided.