Refactoring generic instantiation is valuable for improving reusability and type safety of software. Most of the existing approaches of refactoring legacy code are not suitable for on-line and persistent refactoring because of their complexity. This paper proposes an instantiation refactoring approach for Java programs based on an extended variable type analysis algorithm. A generic type propagation graph is constructed, and new constructs used to express generic type analysis are added to the graph, so it is suitable to do a generic variable field sensitive type analysis. The paper also discusses how to use alias information to improve the refactoring. The case study shows that the results are satisfactory.