Abstract: Ground subsidence monitoring is costly if we use dual-frequency GPS receivers for all stations while positioning precision will decrease if we use single-frequency GPS receivers for all stations, as first-order term ionospheric error cannot be eliminated by combining observations. To solve this problem, we use a single-and dual-frequency mixed mode for subsidence monitoring. We get the residuals for atmospheric delay error by processing dual-frequency stations around the subsidence monitoring region and use the residuals to correct the single-frequency monitoring station observations. This mixed mode approach reduces hardware costs and improves the positioning precision. We processed real subsidence monitoring GPS data based on software developed by the authors. Numerical results show that the precision in the U direction was better than 1.24 cm, three-dimensional position precision was better than 1.59 cm, and precision was improved 24% overall using the single dual-frequency mixed mode. Furthermore, the precision results were better when single frequency monitoring stations are located within the dual-frequency station region, the precise in U direction was better than 0.95 cm, three-dimensional position precision was better than 1.2 cm, precise improved 30% overall and in the best case conditions, improved to 58%.