Abstract: A full-time solar desalination system composed of the trough solar collector and multi-stage flash device is proposed. The average production of distilled water of this system is 3000 m~3 per day. By the simplified algorithm of multi-stage flash process,the dynamic simulation is accomplished by TRNSYS software under the climate of Shanghai. The life cycle cost analysis is adopted to compare the economy between the designed system and a desalination system driven by conventional energy. The results indicate that the average solar fraction per year is 41.11% for the solar desalination system. Throughout the life cycle,the unit desalinated water production cost of the proposed system is 18.48 yuan/m~3 in Shanghai. The solar desalination system has better economic performance than the conventional energy desalination system of the same scale,when the inflation rate is under 8.5% or the gas price is beyond 2.09 yuan/m~3.