Abstract: Based on the electricity demand characteristics in deregulated retail market, a joint equilibrium model in both wholesale electricity market and retail market was proposed. It is used to illustrate the effect of deregulation in electricity retail market on wholesale spot market. According to the demand load profile, different relationships between retail price were wholesale spot price were simulated for peak load period and valley load period respectively. Then, the joint equilibria in both wholesale electricity market were retail market were derived under completely deregulated retail market and partly retailside regulation. The numerical result shows the effectiveness of the proposed model. It points out that deregulation of retail market will reduce the total electricity demand, decrease the spot market clearing price, and make the electricity demand more elastic. It also can be concluded that more competitive the retail market is, less effect of fixed retail price but larger effect of demand elasticity will be on the spot market clearing price.