Operations of hydraulic excavators require high operation skill and operators have possibilities to work in unsafe environment. To solve these problems, automatic digging control is often studied, but there are few studies focused on improvement of efficiency. A high efficiency digging algorithm for a hydraulic excavator has not been established because the relationship between digging motion and digging performance is very complex. A simulation model which is able to consider interaction between soil and machine would help to establish a digging algorithm for improving energetic efficiency. In this paper, an example for improvement of digging efficiency is shown by our developed distinct element method (DEM) simulation. First, in order to improve the accuracy of the DEM simulation, the parameter identification test is carried out to identify damping ratio and friction coefficient between soil particles. Besides, accuracy of digging efficiency evaluation by the developed simulation is shown by a developed digging test device which can reproduces excavation by hydraulic excavator. Finally, digging simulations are conducted by our suggested automatic digging algorithm. Varying control parameters, influences of control parameters are estimated. These simulation results show that the simulation is able to specified control parameters which promote digging efficiency. Our research evaluates effectiveness of model-based development for automatic digging which enhances efficiency.