We have studied the light propagation properties in an inverted Y-type four-level quantum system coupled with probe, couple and driving fields. Using the numerical simulation method, we investigate the absorption properties of the probe light field when the Rabi frequency and detuning of the driving field are changed. From the three-dimensional graphics, we find the variations of the probe group velocity at the electromagnetically induced transparency windows. Farthermore, we theoretically obtain the conversion among subluminal, vacuum and superluminal light propagation by adjusting the Rabi frequency and detuning of the external driving field properly.