Soil-vehicle interaction problem is important for predicting trafficability of off-road vehicles. Tractive forces applied to the wheels due to contact with soil can be estimated by soil deformation analysis around the contact area. In this project, soil movement under a rolling wheel was observed as references for the validation of constitutive models of soil deformation analysis and the construction of numerical analysis methods. A rigid aluminum wheel was rolled on flatten dry sand in a slender bin with the same width of the wheel. The side wall of the bin is transparent so that the movement of sand particles under the rolling wheel can be observed through the wall in plane strain condition. To make it easier to capture the sand particle motion under the wheel by a video camera fixed in space, the position of the wheel is stationary in the longitudinal direction and the sand bin is inversely forced to move backward. Changing the combination of the wheel rotational speed and the sand bin longitudinal speed enables various slip ratios for the experiments. The motion image stored in a PC is processed by the method of a particle image velocimetry (PIV). PIV method reveals the sand particle motion under the rolling wheel, which might be useful for the deformation analysis of soil. Several patterns of sand flow were obtained on the wheel slip ratios. The results of sand flow analysis were used for the validation of a finite element method constructed for wheel-sand interaction problem. The numerical frame of the finite element that moves in space at the same longitudinal velocity of the wheel independently from sand particles was tested for its validity. Numerical results were compared with the velocity field obtained by PIV to modify the numerical code.