The extension & compaction scanning algorithm based on LTI (Linear Travel-time Interpolation) ray tracing algorithm can properly trace the ray path of the direct wave, diffraction wave and echo's, but it has the following problems: low computational efficiency and slow convergence speed. Aiming at these problems and using the cross-scan mode to improve the algorithm, an improved extension & compaction scanning algorithm based on the cross-scan mode was presented. Theoretical analysis and the results of numerical calculation show that the improved algorithm not only maintains all the advantages of the extension & compaction scanning algorithm, but also has a higher computational efficiency. When the model is mesh more refined，the advantage of the improved algorithm is more significant in computational efficiency.