Anchor plate is a necessary component of the prestressed rock bolt, which plays a decisive role in actively resisting the rock mass deformation and improving the self-bearing capacity of the surrounding rock. In this paper, in order to investigate the effect of anchor plate on the mechanical behavior of prestressed rock bolt used in squeezing large deformation tunnel, a series of numerical, field and laboratory tests were performed. The mechanical characteristics of anchor plate with different shapes and sizes were systematically analyzed. Based on the Muzhailing Tunnel in Gansu Province, China, which is a typical deep-buried soft rock tunnel and suffered from serious squeezing large deformation disaster, the field verification was carried out. Meanwhile, the influences of spherical washer on the mechanical behavior of bolt shaft and anchor plate were also investigated. The result shows that the bowl-shaped plate has much better performance than the flat one, while the rounded bowl plate performs slightly better than the squared bowl plate. With the increase of plate thickness or plane size, the anchor plate has the better bearing capacity, while the stress transfer effect will be worse. Furthermore, the non-uniform deformation will gradually increase with the decrease of plate thickness or increase of plane size. Therefore, it is advised to increase the plate thickness rather than the plane size under the condition of better bearing capacity. The bending-induced stress of the anchor plate increases rapidly with the increase of the inclination angle between bolt shaft and anchor plate. Whereas the installation angle is unavoidable in practice, the spherical washer which has great effects on reducing the bending-induced stress could be a necessary component of the prestressed rock bolt system.