The research and development of protection control in intelligent distribution network become the inevitable outcome and the development trend of electric power system with the increase of demand in power supply demand, increased strength of connection complexity and access of renewable energy access. This paper puts forward the method of distribution network centralized differential protection based on the concept of generalized node in distribution network. It applies the concept of generalized node to determine the minimum differential interval of differential protection, namely the minimum set of electrical components composed by the protection terminal and being in closed and encircled status, according to the power grid structure and real-time measurement available. This paper establishes the mathematical model based on the generalized Kirchhoff's law , and gives the calculation method. Numerical results of calculating examples show that the proposed algorithm is feasible and the method can solve the problems of DG access and the protection of the distribution network included the ring network circumstances.