Integrated optical devices have been used in many areas. For all optical devices, a great challenge is the coupling between fibers and devices, because the alignment tolerances required for coupling is stringent. This is an area that has received much attention. The most common coupling method is to use precision etched Si V groove as the fixture of tail fiber of integrated optical devices. The quality of V groove is essential to the success of the coupling of tail fiber. The theory, design and process about the fabrication of Si V groove is discussed.