Abstract: Virtual reality technology provides an effective method to assembly module fixture.Because of universal and normative characteristic of module fixture，marked method can be the base of precise position and assembly relation.As the geometry assembly relation base of the fixture module in VR，mark is built on the function surface，and oriented the fixture based on the mark.The system manages the database as three layers：part，subassembly and instance，and the restriction relation is built on the base of mark.Using the mark，design efficiency is improved and design knowledge and experience can be saved and reused.A example is used in virtual assembly sysyem.