Author designed and developed a serpentine-flow flat-plate solar collector of small volume and large temperature difference in order to explore the flat-plate solar collector used in high temperature situation. And carried out experiment of stagnation and instantaneous efficiency. The results shown that stagnation temperature can reach 170.2 ℃ and heat loss coefficient is 5.239W / (m2.℃). Efficiency of solar collector between 52% -55% when inlet temperature of working fluid is70 ℃. By comparison the temperature trend of various parts of the collector then proposed the corrective measure to improve performance of serpentine-flow flat-plate solar collector in high temperature conditions.