In this paper,we study the dynamics of twocoupled preBtzinger complex with calcium ion current.By phaseanalysis,bifurcation and fastslow decomposition,we investigate the effects of the intracellular Ca2+ concentration and the calciumactivated nonspecific cationic current (ICAN) on the firing activities of preBtzinger complex,and explain the generation and transition of the bursting activities.The results show both the periodic oscillation of Ca2+ concentration and dynamics of ICAN will decide the types of firing activities,and the periodic oscillation of Ca2+ concentration is the key factor of complex bursting.