Abstract: While avoiding any compromise on the flexibility of assembly for phase change energy storage unit in solar energy storage devices,the structure of ordinary rectangular plate unit was optimized to enhance the heat storage performance of plate phase change unit,a new type of trapezoidal unit was designed,and the theoretical solution to optimal trapezoid structure was obtained through theoretical analysis. Besides,the results of theoretical analysis were verified by means of experimentation,suggesting that the designed new trapezoidal plate unit is not only capable of enhancing the heat storage performance of energy storage device by taking advantage of the melting characteristics of the phase change material,but also effective in improving the rate of space utilization. As far as this study is concerned,the increase in the flow rate of the heat exchange fluid and temperature rise are effective in improving the efficiency of heat exchange for the unit. To be specific,when the flow rate reached 0.12 m/s,the optimal trapezoidal unit showed a more significant sign of improvement in heat storage performance than the rectangular unit.