The development and evolution of tropical cyclone (TC) "Soudelor" (2015) was simulated using the Weather Research and Forecasting model (WRF). The simulation well reproduced the path, intensity, circulation, cloud system evolution and rainfall of "Soudelor". The three-dimensional surface rainfall equation was applied to quantitatively diagnose and analyze the precipitation process of "Soudelor" when it moved over the ocean. The results show that Q_WVA (the three-dimensional moisture flux convergence or divergence rate) played a major role in the variation of the rate of change for moisture-related processes (Q_WV), which was related to precipitation inside the TC circulation. But Q_WVL (vertically integrated negative local change rate of water vapor) and Q_WVE (surface evaporation rate) also made important contributions (especially the latter). Although the contribution of Q_WVE was significantly less than that of Q_WVA, water vapor that converged outside the circulation might be mainly come from the evaporation of sea water in different areas outside. Thereby, the overall contribution of sea surface evaporation should be great. The characteristics and variations of Q_CM (the rate of change for cloud-related processes) were more complicated than that of Q_WV, and Q_CLL (vertically integrated negative local change rates of liquid-phase hydrometeors) inside the circulation maintained positive (liquid-phase hydrometeors continuously decreased) throughout the incipient stage. Liquid-phase hydrometeors were largely consumed by converting into ice-phase hydrometeors and feeding the surface rainfall as well as by three-dimensional flux divergence. Q_CIL (vertically integrated negative local change rates of ice-phase hydrometeors) mainly stemmed from microphysical processes and surface precipitation before 0400 UTC 6. The flux convergence from the outside circulation also had certain effects after 0400 UTC 6. With increased surface rain rate, the transient growth of cloud hydrometeors (negative Q_CLL and Q_CIL) were mainly attributed to the ascending motion that enhanced markedly and expanded vertically. Cloud hydrometeors increased obviously with the sharply enhanced upward motion. Melting of graupels (P_gmlt) and accretion of cloud water by rain (P_racw) were two main sources of raindrops. Regionally and temporally averaged precipitation efficiency inside the TC circulation was as high as 96%. Q_WVA was the main contribution term, while Q_WVL and Q_WVE also made important contributions, which was related to the underlying ocean surface where the TC was located. When the TC moved over the sea, both the abundant source and the small sink for surface rainfall led to the high precipitation efficiency. As the main source of raindrops, P_gmlt accounted for 72% of P_racw, which reflected the characteristic of active deep convection inside the TC circulation during this period.