A collective rhythm emerges in suprachiasmatic nucleus(SCN) of mammals hypothalamus, controlling the central nervous system and peripheral tissues. To explore the emergence of circadian rhythms, a modified Kuramoto model of the SCN network is established, and its phase synchronization is analyzed. The results show that emergence of circadian rhythm is expressed by phase synchronization. The effect of parameters on order parameter is studied, showing agreements with biological facts. This study provides insi...