Abstract：To improve the design approach of anchor plate supporting slope，the calculation formula of anchor plate size is proposed according to the internal balance of slope，and the formula of safety factor of unsaturated anchor plate supporting slope is obtained through the variational method combining limit balance method. By using transient seepage to simulate rainfall conditions，the variation rule of slope safety factor with rainfall time was obtained，and the internal mechanism of slope safety factor variation was analyzed. The results of safety factor are compared with the results of existing methods by 4 examples，and the rationality of the suggested formula is verified. The effects of rainfall intensity，seismic conditions and anchor plate supporting conditions on slope stability and sliding surface are analyzed. The results show that heavy rainfall and earthquakes will significantly reduce slope stability. Horizontal and vertical seismic forces will lead to deeper sliding surface，while vertical downward seismic forces will lead to shallower sliding surface. The proposed approach can not only calculate the safety factor of saturated and unsaturated slope，but also calculate the safety factor of slope under transient seepage and steady seepage，and has strong applicability. In order to facilitate the engineering application，by comparing the slope safety factor when the anchor plates are arranged at different vertical spacing，the vertical 3m spacing arrangement of the anchor plate is given as engineering suggestion. A simple method for the size design of anchor plate is presented. The size of anchor plate obtained by the simple design approach is much lower than the existing empirical design size.
