In recent years, software programs are widely used in many safety-critical systems. These systems do have high reliability targets and hence it is necessary to analyze these programs. Also, the complexity of such programs must be very low, which can be ensured by analyzing the dynamic coupling between the functions. We propose call graph construction of a program for such analysis. It also proposes method to partition program graphs for reducing the complexity of the system, which also helps to bring out the system composition. The robustness of the method is shown from an implementation of the algorithm.