This paper proposes a method based on the features of UML(Unified Modeling Language) use case diagram and sequence diagram by risk analysis techniques and using probability of use cases.One component is selected as core in each use case according to this component using probability and risk degree.To implement integration testing of whole system

the component with the highest using probability and the highest risk is regard as the core

the other components are gradually involved step by step according to sandwich integration testing.This testing method can control the risk of system and implement a part of reliability testing.