In this study, we modeled a ship or marine structure into a rectangular resistance body and tried to examine surrounding flow characteristics and pressure distributions behind the resistance body experimentally and investigated pressure characteristics by a 3-dimension numerical simulation. As a result, the reattachment point of the mainstream separated from the upper part and proceeding to the rear part was about x/H=6, but by the influence of the negative pressure area formed behind the resistance body and interference of the flow flowed in winding from left and right, the reattachment point of some flows was formed near x/H=1.33. The perpendicular velocity component behind x/H=0 varies in size with the recycle flow shapes formed from the influence of the resistance body, but generally it shows a negative distribution and there is a decreasing pattern as it goes to the down part. We verified the result of the calculation by comparing the velocity distribution of 3-dimension numerical simulation using a commercial software and the PIV(particle image velocimetry) measurements. In the numerical simulation results, the static pressure characteristic behind the resistance body was proportional to the inflow velocity, and the dynamic pressure shows a similar pattern with constant-velocity from the experiment.