The selection of soil foundation bearing capacity for deep excavated spillway is very important for spillway design, because it is related to the design of side wall supporting and retaining structure and spillway floor reinforcement.This paper analyzed the difference in the codes by combining the loess foundation engineering of stilling basin of a reservoir spillway in Shaanxi.The suggestion is that it doesn't need to correct width plate and excavated deep for side wall supporting and retaining structure and spillway floor, because they have different stress mechanism with building's overall instability. Meanwhile, because the loading after unloading modulus of soil is much higher than the loading modulus and the size of load board is small in loading test, the foundation bearing capacity by loading test only reflects the value of expansive area after unloading and is lower than practical bearing capacity.So it is suggested that foundation bearing capacity by loading test should be compared with gravity stress of original overlying soil for foundation excavation depth more than 5m.The foundation bearing capacity should adopt the value of gravity stress of original overlying soil when foundation bearing capacity by loading tests is lower.