Many times for repeated computation are needed in optimized back analysis, which will spend a number of hours if the scale is large. For overcoming the shortage, the ultimate cause is analyzed. From the objective function, the improved format is put forward and its solution is proposed. Then, the new method for integrated deformation modulus back analysis is developed on the basis of the improved format and the genetic algorithm. Taking Xiaowan Hydropower Station as the engineering example, the excavation FEM model is built, and the deformation modulus for the dam base obtained. The calculated result proves that the efficiency can be enhanced greatly by the new method. In addition, other new methods can also be developed on the basis of the improved objective function with other optimized algorithm.