To improve the pull-out bearing capacity of the anchor plate support system, a support system with series-connected anchor plates was proposed. Based on the Winkler foundation model, a theoretical analysis method for the pull-out resistance–displacement relationship of the series-connected rectangular anchor plates was established through the force equilibrium and displacement continuity conditions. The model experiment of square anchor plates buried in cohesive soil was carried out, and using FLAC3D.6.0 software, a numerical simulation model of the anchor plate was established. Combining the experimental and simulation results, the approximate analytical solutions for the pull-out resistance–displacement relationship of the series-connected square anchor plates were obtained. The on-site experimental results concerning the pull-out resistance–displacement relationship of anchor plates from three engineering cases indicate that the pull-out bearing capacity of the anchor plate, as obtained by the C and M methods in this paper, surpassed the measured capacity. Furthermore, the application of the T-method was considered more rational. The research also indicates that the critical depth between deep- and shallow-buried anchor plates is approximately 4b; for series-connected square anchor plates, to avoid diminishing the pull-out bearing capacity of the support system, the minimum spacing between adjacent plates should satisfy L ≥ 4b.