To rationalize open-cut construction by eliminating or reducing the cut beams, the double sheet pile method with a fixed head was developed as new earth retaining method. To develop the design method and clarify the behaviour of the soil between two sheet piles (referred hereafter as 'inner soil'), a numerical model using the discrete element method (DEM) was developed to observe the behaviour of the sand sandwiched by two sheet piles. Firstly, the density and triaxial compression tests were conducted to model the general friction angle of sand. After that, using the parameters set which were calibrated by the triaxial test on DEM, a horizontal loading test was conducted with two sheet piles and the inner soil and compared with the experimental results. By these, it is confirmed that this model can reproduce the results of the experiment. Moreover, analysis of the stress state during loading reveals how the stress state of the inner soil changes. Developing this model allows us to consider the soil-structure interaction problem in this method from the aspect of numerical analysis and to think of various construction conditions for more rational design and construction.