Abstract: The mechanical mechanism of geogrid-encased stone columns is complex, and the characteristics of the geogrid have an impact on their bearing capacity. Based on the theory of cavity expansion and the assumption of the soil pressure of the edge of single-pile effective reinforcement as the static soil pressure, the method for calculating the bearing capacity of composite foundation is obtained. Combined with the engineering examples and existing research achievements, the results show that this method is more consistent with the actual projects. Finally, on the basis of this method, the analysis demonstrates that the optimal reinforcement depth of geogrid-encased stone columns is not a fixed value, and it changes with material properties and soil conditions.