With the development of electric power industry, more and more projects of building transformer substation need a great deal of fund. More exact evalution of projects becomes more important.In evalution of projects, calculation of earthwork volume may be a very important part.According to the requirement of most projects and on the basis of traditional method , we have created a new method of optimal calculating earthwork and auto-balance. Minute-dividing technology and interpolating way are used to enhance the simulation of Grids.The new method can better simulate the landform and more effectively promote the precision and speed of calculation of earthwork .Auto-Balance can do what can't be reached by manual work.