Adaption of circadian rhythms in behavioral and physiological activities to the exteal light–dark cycle is achieved through the main clock, i.e., the suprachiasmatic nucleus (SCN) of the brain in mammals. It has been found that the SCN neurons differ in the amplitude relaxation rate, which represents the rigidity of the neurons to the exteal amplitude distur-bance. Thus far, the appearance of that difference has not been explained. In the present study, an alteative explanation based on the Poincaré model is given which takes into account the effect of the difference in the entrainment range of the SCN. Both our simulation results and theoretical analyses show that the largest entrainment range is obtained with suitable difference in the case that only a part of SCN neurons are sensitive to the light information. Our findings may give an alter-native explanation for the appearance of that difference (heterogeneity) and shed light on the effects of the heterogeneity in the neuronal properties on the collective behaviors of the SCN neurons.