Abstract: Gravity anomaly continuation from undulating surface to plane can provide gravity data on a flat horizontal plane for frequency-domain data processing and inversion. Based on the theory of conventional interpolation-iteration methods, this study proposed a modified interpolation-iteration method by introducing a correction factor of the undulating observation surface in the iteration and correction process. The improved method accelerated the iterative convergence speed and promoted the continuation effects. The theoretical model-based tests show that this method can be used to achieve stable and effective large-span gravity anomaly continuation from greatly undulating surface to plane. The continuation results presented by this method are better than those obtained using conventional interpolation-iteration methods. The application of Bouguer gravity anomaly data of the Sichuan-Yunnan region demonstrates that the modified interpolation-iteration method effectively enhanced anomalous signals and details and can provide reliable data for subsequent processing and interpretation.