Abstract: In order to make more reasonable connection capacity planning of power distribution network line, a refined research method for connection capacity planning of power distribution network line is proposed based on the full use of "one library and three centers" (unified data repository, statistical distribution center, center of mathematical analysis and decision-making center) in this paper. First, the customers of power distribution network are classified to analyze the load characteristics of all kinds of customer. Next the development stage of distribution network customers is analyzed by fast clustering analysis method. Then a calculation method for determining the planning connection capacity of distribution network line is given based on the simultaneity rate and the demand coefficient of loads. Finally, an actual distribution network line planning case is given to demonstrate the basic features of the method proposed.