In the attempt to apply static analysis method to API (application programming interface) conformance validation, It is noticed that the gap between numeric value based temporal properties in API specification and variable symbol based predicates extracted through static analysis. Therefore, the paper first investigates value equality relations between variable symbols in C program, and then designs an ECS (equality class space) based value equality analysis method. This flow-sensitive method can maintain the correspondence between variable symbol domain and numeric value domain during the process of API conformance validation, and in addition, can effectively support the optimization of subsequent analysis by hiding all irrelevant information except value equality relations.