Abstract: In order to investigate the homogeneous bank caving of reservoirs during the first impounding, 9 bank slope models divided into 4 types are made in the laboratory. The model test results indicate that the larger the angle of the bank slope, or the smaller the particle size in the bank slope, the more possible the bank caving. The collapse of the convex bank is easier than that of the concave bank. The larger the angle of the underlying bedrock, the more possible the bank caving. The typical phreatic lines in the model slope obtained from the experiments are compared with those obtained from a published analytic solution. The comparison indicates that the published analytic solution may over-estimate the elevation of the phreatic lines. The over-estimation may result from the neglecting of the unsaturated state of the bank soil mass in the analytic solution.