Solar domestic hot water system is widely used and developing fast in recent years in China. However many problems occur at the same time, for example more energy consumption by circulation pump, water reheating, long investment payback period, and etc. Through analyzing the field-testing data of projects and investigating of different residential consumers, it was found that compared to actual hot water consumption the solar domestic hot water systems were generally designed too large in capacity, which means the designed hot water demand is much greater than actual user consumption. This study compared different specifications and recommended design parameters value of hot water related standards, and analyzed the calculation methodology and design parameter ofhot water quota. Finally problems in the system design are summarized and suggestions are proposed for designers and different stakeholders.