In the field of freshwater and seawater, through research with particular emphasis on the cause of formation of solar pond, rate of salt-diffusion, thermal stability, operation mechanism of solar pond, negative effect of solar pond, etc., the operation theory of zero-gradient solar pond was put forward, and under the direction of the theory, by taking use of the combination of the method of upwards-spray, infiltration and convection, we completed the research on operation technology of zero-gradient solar pond and achieved many inspiring research outcomes.