The invention mainly discloses a solar water purifier for lakes and a water purification method thereof. According to the technical scheme, the solar water purifier comprises a main body, a purification system, an energy system, a drive unit, a lighting device and a fixation device. The energy system comprises a solar cell panel, a storage battery and a charging panel. An oxygenation chamber, a disinfection chamber and a purifying chamber are arranged inside the main body. An ozone generator, an air compressor, a bubble generator and an aerator pipe are disposed inside the oxygenation chamber. A drug blending tank is arranged inside the disinfection chamber. A purifier is disposed inside the purifying chamber. When the device operates, installation and pilot run of the device are firstly carried out. After successful pilot run, the device is put into a lake. By mobile positioning of the drive unit, a water body undergoes disinfection, oxygenation and purification. The energy system provides energy. Thus, energy is self-sufficient. The solar water purifier has a simple structure, is low-cost and clean. By various purification methods, purification efficiency is high. By the floating and stationary combined design, position of the device can be controlled freely. Thus, repair rate of water body is high. The solar water purifier is easy to operate.