Considering the whole process of the cushion from the excavation to backfilling, we constructed the optimization utility model for replacement sand cushion under consideration of code as constraint. According to this model, we analyzed the impact of different standard values of bearing capacity of sand cushion against the optimal results by an example. The example shows that compared with the trial algorithm design, the use of this optimization method can not only reduce the amount of sand cushion filling but also be able to directly derive the optimal pit excavation volume.