Abstract: In order to find out the best additive portion of soft foundation treatment for a petroleum storage project located in Guangzhou Nansha harbor area, the typical soft sludge was selected and solidified experiment was conducted with the additive agent of cement, lime, gypsum, sodium silicate and water-reducer, and the treatment result and the best additive portion were got, the changes of the mechanical properties and microstructure of the soft sludge before and after consolidated were compared and studied based on the unconfined compressive strength. Test results show that 20%, 1.5%, 10%, 6% and 16% of cement, lime, gypsum sodium silicate and water-reducer are the best proportion, and among these 5 factors affecting the strength of the solidified soft sludge, the cement addition has become a most important influence factor and the gypsum addition is the minimum. Comparing with unconsolidated sludge soft sample, the penetration coefficients and void ratio of the best additive portion solidified sample are reduced by 81.0% and 59.8%, and C and φ of UU shear tests are of 3.8 and 4.9 times. The physico mechanical properties of the solidified soft sludge are enhanced obviously.