There are great differences in action potentials between the Purkinje fiber cell and ventricular muscle cell. In many conditions, Purkinje-ventricular junction is considered as the source of serious ventricular arrhythmia. An idealized 2D computational model of ventricular electrical conduction is established to simulate the coupling junction of Purkinje fiber and ventricular tissues as well as the excitation conduction in the cardiac tissue. Simulation results show that the Purkinje fiber cells can generate the conduction of electric excitation in tachycardia and also can suppress excitations in extremely slow or fast rhythm. The Purkinje fiber plays an important protective role to keep ventricular tissues in normal rhythm. This model provides a new method to research the mechanism of arrhythmia and also can be used to study arrhythmia induced by congenital gene mutations and effects of antiarrhythmic drugs.