The main purposes of comparison based qualitative simulation are predicting the system's behavior deviations caused by perturbations in its parameters and the initial state and giving the explanation. This paper proposes a method of comparison based qualitative simulation CQSIM. It is based on the achievements of Weld, Neitzke and Neumann. It implements the comparison of according parts with the suitable observation caliber, the qualitative simulation of one or more deviations and the analysis of changes in the behavioral topology.