A method for forming a low loss dielectric layer in the tungsten chemical mechanic grinding process is disclosed. After forming a dielectric layer on the semiconductor substrate and smoothing the dielectric layer as an inner dielectric layer, a stop layer of undoped silicon dioxide, organ spin on glass, or silicon oxygen nitride are coated thereon. After process of plug lithographic and etching, a barrier layer of tungsten plug and metal tungsten are deposited sequentially. Finally, the surplus tungsten metal layer on the surface of a dielectric layer is removed by chemical mechanic grinding process until the stop layer is exposed. In the present invention, the stop layer is used to repair the scratches or defects generated from the smoothness in the chemical mechanic grinding process. Furthermore, in the tungsten chemical mechanic grinding process, it can assure that the inner dielectric layer will not be ground so that the object of low loss is achieved.