A high efficiency digging algorithm for hydraulic excavator has not been established, because the relationship between digging control parameters and digging efficiency is too complicated. Therefore, we have investigated how digging efficiency is affected by the digging control parameters. In this paper, the digging efficiency is defined by the scooped soil mass per applied digging energy because it is the one of the most simple equation to show the digging efficiency. A digging test device was developed to reproduce the digging behavior of entire hydraulic excavator with using the pre-programmed bucket tip trace. In addition, a digging simulation model by two dimensional distinct element method (2D-DEM) is developed to clarify the digging efficiency with considering some different digging settings. The simulation results are verified by comparing with the test data using the digging device. The digging simulations were performed in order to investigate how the bucket tip trace and velocity effect the digging efficiency. This study shows digging efficiency can be improved by changing tip traces or digging velocities.