Iron core of transformer is a nonlinear inductance component. When this component meets system capacitance, ferroresonance phenomenon may occur. Later, this phenomenon highly distorts the system into over voltage and over current conditions which lead to a fatal destruction of transformer. In this study, two types of iron core had been simulated using ATPDraw to find out their ferroresonance characteristics. MATLAB also had been used to plot the bifurcation diagram during grading capacitance variation. The results showed that the stability of system could more easily be figured out based on the bifurcation diagram. Furthermore, it was pointed out that the transformer with M5 type had better characteristic of ferroresonance responses with 81,08% simulation results were ferroresonance than ZDKH type with 89,19% simulation results were ferroresonance.