Abstract: The GDOP is an important parameter in the navigation system. Yet, along with the development of navigation system from single mode to integrated modes, different systems were integrated into a composed mode system, which resulted in difficult definition and calculation of GDOP and restricted its applications. Based on numerical computation of GDOP, the paper converts the calculation into resolution of different linear equations. The different systems are considered as different restricted conditions. This new method successfully resolved the problem, which could improve the application of the GDOP.