The concept of variantional geometric constraints network is presented. Based on I SO’s feature, three kinds ofvariational geometric constraints are defined. The concepts of mate tree (MT) and loop circuit (LC) are presented. Thegeneration method of well-constrained variational geometric constraints network (VGCN) is studied. The network can beapplied in generation of well-constrained tolerance types and tolerance chains. A simple example is analyzed to show thescheme to be effective.