This paper takes a deep fill slop in Xianning Hubei as the construction background. The numerical simulation software—Geo-studio was adopted to analyze the influence of rainfall-surcharge coupling effect on the stability of deep fill slope， the pore water pressure distribution inside the slope and the influence of constant rainfall and surcharge at the top of slope on the stability coefficient were also analyzed. The results showed that the original slope was in metastable state under the condition of rainfall and surcharge at the top of slope， the stability coefficient decreased with the rainfalls time， compared with the constant rainfall， the surcharge load had a greater impact on the stability of fill slope. To the end， a reinforcement scheme of a slope scouring and load reduction and waterproof surface was proposed. The numerical simulation results confirmed the feasibility of the scheme， which meet the requirement of the construction， meanwihile， the rationality and validity of the simulation results were verified.