Abstract: Objective: This study aims to address the inherent system errors and strong coordinate coupling issues in traditional deep-space network measurements for lander positioning. A new method for combined orbit determination and positioning of lunar relay satellites and landers is proposed to improve the accuracy of lander localization. Methods: First, the theoretical application of four-way relay measurement data in combined orbit determination and positioning is described, and its potential to improve positioning accuracy is analyzed. Second, an optimization scheme integrating both local and global parameters is introduced. This method effectively utilizes long-term observation data to achieve an optimal overall estimation of the target parameters. To evaluate performance, simulation experiments are conducted comparing independent and alternating observation modes. Results: The simulation results indicate that the alternating observation mode significantly enhances the accuracy of both orbit determination and lander positioning. Furthermore, it is observed that different landing regions have varying effects on the performance of orbit determination and positioning. Conclusions: The proposed combined orbit determination and positioning method, particularly the alternating observation mode, offers an effective solution to the limitations of traditional deep-space network measurements. The results indicate that variations in landing regions have a measurable impact on positioning accuracy, providing valuable insights for future deep-space exploration missions. Future research should focus on optimizing observation strategies according to regional characteristics and exploring the applicability of this method in more complex deep-space mission scenarios.