photovoltaic system, optimum tilted angle, siphon principle, water treatment Abstract. Based on the recent research at home and abroad and the local meteorological data, this study aims to determine the optimum tilt angle of the solar-cell array surface and the best month on the system to achieve the optimal design of PV system. Full mechanical automatic control system is designed by using lever principle and siphon principle to realize the purpose of all-day and maintenance-free operational situation. It can replace the motor control system and at the same time，enjoys reliability, low cost, long life and energy conservation. The indoor and local river data of the experiment shows that this system has an evident effect on water decontamination. Furthermore， comparing with traditional aeration system. It has many advantages, for instance, it can save more than 20 thousand and carbon emission can be reduced by 683 ton and other aspects.