A concolic execution based testing framework is proposed to generate tests for real-life applications. Concolic execution is a hybrid software analysis technique which combines concrete execution with symbolic execution. It makes some tradeoff between pure static analysis and dynamic analysis. Existing concolic testing tools are mostly targeting programs with sources, and nontrivial dependencies on application development tools are introduced thereby. In our work, we built a concolic execution tool that directly targets program binary. Therefore, it can generate test cases without the presence of program source, and does not incur unnecessary dependances on the application development tools. Depth First Search algorithms are integrated into the test case generation process to explore the test space. Experiments show that concolic execution based test case generation process is effective in both achieving good coverage, and uncovering errors.