In the analysis of function, which is the core and early phase among the procedure of construction VE Job Plan, the accuracy of function definition directly connects to VE result. However, the method of defining function, which is currently used is not accurate and comprehended or is difficult to utilize it systematically. Also, there is not a clear definition about the function for selecting VE so that many difficulties occur in the organic connection between each of functions in the summarization of function after defining function. Therefore, this study cleared the definition of function and made up any counter measured problem occurred in FAST Diagram later on and suggested CAFAT(Combined Antithetic Function Analysis Technique) in order to induce better phase in functional analysis.