On the basis of bending forming force and deformation analysis for a stainless steel part in a precision instrument, the combination mould having filling and support function was designed for the part with large size, ultra thinwall and nonclosed cross section structure characteristics. Combined with the forming process, the technological measures were proposed to eliminate the bending forming deformation by using the way of incremental forming control and the gap control between mould and part. And the forming process and the reliability were verified by practical application.