Bending experiments of middle thick plates of three materials were done under a series of conditions. The same processes were analyzed with FEM numerical simulation. The simulation results inosculate with the experiment data well. The thickness reduction ratios of the samples are arranged in 0.5%-4.5%.The transient stress fields during the processes were obtained as well, and the displacement rule of neutral layer could be learned from them. The results show that FEM numerical simulation can be very useful to further research and manufacture of middle thick plate bending process.