For the periodically excited Chens system, when there exists order gap between the natural frequency of the original system and the excited frequency, dynamical behaviors associated with the two different time scales can be observed. Bifurcations of the system have been presented by considering the variation of the excited term. Fast-slow analysis is employed to explore the evolution of the system with different parameter conditions, which gives different types of bursters such as symmetric fold bursting, symmetric subHopf bursting and symmetric Hopf-homoclinic bursting, as well as the bifurcation mechanism. Furthermore, the influence of both the amplitude and the frequency of the excitation on the bursting is discussed in detail.