The global coordinate reference frame is one of the most important infrastructures for the development of global satellite navigation system, but also an urgent demand in China's construction of spatial information facilities. This paper focuses on the mathematical model for a Global CGCS2000 Coordinate Frame, analyzes the theory and algorithm of the inner constraints required for Global CGCS2000 Coordinate Frame formulation, and shows that under certain conditions, a two-step method and one-step method are identical. The Inner constraints algorithm redefines the constraint conditions of the coordinate reference frame according to minimum standard for parameter transformation and its rate. Coordinate similarity transformation yields an adjusted network, which ensures the highest degree of fit with the initial network shape, maintaining the coordinate network from the effects of different observation technologies. The results of this study can deepen the theoretical foundations of coordinate frame determination, and provides a scientific method for the realization of the CGCS2000 globalization.