An anchored sheet wall is commonly used in retaining deep excavations. Anchor force is one of the critical design parameters in practice. Based on the kinematical admissible failure mechanism, a limit analysis approach to determine the anchor force is presented. The explicit formula for the anchor force is given, which makes it easy to calculate using a simple calculation program such as MS Office Excel. Anchor force is mainly influenced by seven parameters: the internal friction angle; cohesion of the soil; wall friction angle; surcharge on the ground surface; dip angle of the anchor; penetration depth of the wall; and depth from the anchor force action point on the wall to the ground surface. The relevant quantitative calculation can be performed by the proposed method. In addition, the design anchor force under a specified design safety factor and the anchor forces of multiple rows of anchors are also illustrated in this paper. To verify that the method is reasonable, the predicted and measured anchor forces are compared in two classical soil-nailed wall experiments. The result shows that the presented method is applicable.