For process assignment that is strongly cohesive and weakly coupled, an evaluating model based on activity relation matrix is constructed on the similarities between software programs and the process. In this model, activity relationship matrix is employed to describe constraint-dependent relationships among activities, and this matrix is presented for calculating the numbers of controlling elements to improve the efficiency and rate of getting cohesion coefficients. In additional, the inspiration for the introduced notion is derived from cohesion metrics in software engineering. Also, a heuristic qualitative analysis method is provided that is based on this model to decide between various process assignment alternatives. Both a theoretical and an empirical evaluating method give a positive support its soundness. Lastly, three examples are given to verify the feasibility and effectiveness of the model.