Water thermal stratification exists in the discharging process of solar storage tanks, and a high efficiency of thermal stratification can greatly improve the discharging performance of solar tanks. The water tank with dimensions of 0.8 m (height) × 0.4 m (width) × 0.4 m (length) and three kinds of inlet structures were investigated in this study. The inlets included a perforated inlet, slotted inlet and direct inlet. The discharging performance of the tank was studied by presenting some compared experiments. The dimensionless discharging time was defined to analyze the temperature change of top-layer and inter-layer of water. Quantitative analysis and comparison based on the effective discharging efficiency and carbon reduction in the tank with different inlet structures were carried out in this study. The results indicated that the perforated inlet and slotted inlet improved the performance of thermal stratification effectively. The effective discharging efficiency of the perforated inlet structure was 21% higher than that of a direct inlet with the flow rate of 5 l/min and the gap increased to 40% when the flow rate increased to 15 l/min. The application of the perforated inlet tank in the discharging process in all solar water heaters in China can provide a CO2 reduction of 5.39 × 104t compared with the direct inlet tank.