Infeasible paths are one of the most important parts to cost the test resources.Before path testing

infeasible paths detecting in a program can save test resources efficiently.This paper presents a static method to detect infeasible paths which is based on sub-path expansion.First

the proposed method generates sub-path set

and the feasibility issues will be converted into inequalities.Second

the constraint solver is used to solve the inequalities

and then we can distinguish the sub-paths into three parts:one part is infeasible sub-paths

the second part is feasible sub-paths

and the third part is undetermined.The paths that are expanded from the latter two parts will be tested again to determine their feasibility.Eventually

the feasibility of all the paths is detected.Most of the detecting work is on sub-path set

so our method makes an effective solution to the path-explosion problem.Experimental results show that the proposed method can detect infeasible paths more accurately and effectively.