Abstract: Time-depth conversion is one of the key steps in structural interpretation. It includes mainly two categories: constant-velocity mapping and variable-velocity mapping. The constant-velocity mapping is not suitable for a work area whose lateral velocity field changes intensely. The key point of this paper is to establish a time-depth conversion method that is suitable for the field with variation of lateral velocity and in accordance to the geological characteristics, for which an iterative variable velocity mapping technique was developed based on the inversion of superposition velocity, and the results of hydrocarbon detection were integrated. The iterative mapping technique was applied to the mapping of various complex underground structures, and the results are consistent with the distribution of hydrocarbon and geological implications. In addition, by using the iterative mapping technique, the controversy between structural gas reservoir area, "bright spot" area in the A Gas Field was well solved, and the geological reserves were expanded, and the construction and development of A Gas Field was effectively promoted.