Based on the characteristics of lake’s dredging sludge, i.e. high organic content, high water content and low strength, this paper investigates solidification tests with cement, lime and fly ash as improving additive. Proceeding from the changing characteristics of strength and water content after solidification, we study the solidification mechanism of the dredged sludge and analyze the solidification efficiency. According to the fuzzy optimization theory, an optimum model is set up with optimizing scheme of cost, efficiency and time, by which a best project is obtained and analyzed. Results show that the mixture additive of 4% cement and 9% fly ash can be chosen as the optimal scheme according to the model. Due to the mixture addition, the cost decreases about 45% and the shear strength increases to 38%, and this scheme meets the engineering requirements.