Neurons within pre-Botzinger complex have been found experimentally to exhibit different firing activities. One special firing pattern observed in experiment is the so called mixed bursting ( MB ) characterized by combining two or more different types of short bursts within each cycle of a periodic bursting solution. Using phase-plane analysis, fast-slow decomposition, ISI bifurcation, one-parameter and two-parameter bifurcation analysis, we investigate effects of the calcium-activated nonspecific cationic conductance (gcAN) and the maximal SERCA( Fserca ) on the firing activities of the pre-Botzinger complex, especially the mixed bursting pattern. We determine parameter region of Fserca when concentration of calcium changes periodically and propose the generation and transition mechanism of the bursting activities. The results demonstrate that the calcium-activated nonspecific cationic current and Fserca will affect types of neuron bursting and cause mixed bursting.