This paper analyzes the monitoring data of distribution automation management system (open2000) and finds that the average line load rate of distribution grid is low, some of the lines are in the light load or no-load condition, distribution grid redundancy is too high, the overall utilization is low, and the resource is wasted, but while there are parts of the distribution grid line is overloaded, which can not meet the N-1 standard requires and affect the grid reliable operation. To solve the above problems, this paper develops the maximum distribution grid access capacities based on N-1 and load characteristics. It has important reference value to regulate the total capacity of distribution transformer accessing distribution line, guarantee economic operation of distribution grid and reasonable load rate, and meet the requirements of N-1 criterion. It also can be regarded as a calibration standard for access capacity rationality of existing distribution grid.