Based on eight groups of uplift tests for screw anchors with different embedded depths and different plate sizes, a method is given to compute the bearing capacity of screw anchor within critical depth in coarse sand according to analysis on force transmission route and failure characteristics. Within critical depth, bearing capacity of screw anchor is proportionate to embedded depth and the area of screw plate, and the failure surface is inverse triangle in shape. Beyond critical depth, the bearing capacity of screw anchor won’t increase with depth, and the failure surface is funnel in shape. Critical depth is about 10 times the diameter of screw plate. In both cases, the include angle between failure surface and the vertical plane equals to 0.5 time the friction angle of the soil.