Through studying the experimental results on reinforcing soft foundation by vacuum preloading on an airdrome runway in Shanghai City,surface settlement and its calculation method,dissipation of excessive pore water pressure,and reinforcing effects on test zone are discussed. The testing data indicate that the setdement in test zone,from large to small,is observed in center,margin,and corner of site and this reflects the effects of vacuumpreloading method.When vacuum degree changes,the distribution of suction pressure with depth in drained body of test zone is almost equal.The range of suction pressure is 58-65 kPa,i.e.,68%-76%of vacuum degree under seal membrane. Furthermore,the analysis show that the estimation of surface settlement of soft foundation may be carried out through combining vertical equivalent penetration co-efficient,Terzaaghi's one dimensional-consolidation theory,and layerwise summation method.