Abstract: The "improved central-line method", a novel method for dam heightening and capacity expansion of tailings ponds, was investigated to conserve land resources and mitigate the influence of tailings ponds on the surrounding environment. This method is to carry out dam heightening and capacity expansion by employing the middle-line tailings dam construction method based on the original tailings pond that adopts the upstream tailings dam construction method. Based on the original topographic data of the tailings pond, a three-dimensional finite element model consistent with the actual terrain was built by adopting MADIS software. Meanwhile, the numerical simulation method was adopted to analyze the seepage laws of the tailings pond under the "improved central-line method", with the strength reduction method utilized to research the stability of tailings dams. The results indicate that the distributions of the total water head and pore water pressure in the tailings pond conform to the general seepage laws of tailings ponds, and the minimum burial depth of the phreatic line meets the safety requirements specified in relevant codes. Additionally, the anti-slide stability performance of dam bodies in three working conditions all complies with the current specifications, showing the overall stability of the structure. Inheriting the advantages of the traditional central-line dam construction technology, the "improved central-line method" not only achieves effective improvement of the tailings pond’s capacity but also ensures the engineering safety performance by carrying out the collaborative design with the existing upstream dam bodies. The research findings can provide a reference for similar projects involving dam heightening and capacity expansion of tailings ponds.