For a periodically excited fourdimensional nonautonomous system, when the exciting frequency is much less than its nature frequency, dynamical behaviors associated with two time scales can be observed. The excited system can be transformed into a general autonomous system by defining the whole exciting term as a slowvarying parameter. Firstly, the stability and bifurcation conditions of equilibrium points in the generalized autonomous system are presented. Secondly, the slowfast analysis and transformed phase are employed to explore the different types of bursting behaviors with different initial conditions. In addition, the mechanism of coexistence phenomenon is discussed. Meanwhile, delay phenomenon is observed between the points connecting the spiking states and the quiescent states and the bifurcation points obtained theoretically.