The invention discloses a calculation method of power supply capability of a power 
distribution system. The calculation method is characterized in that the 'N-1' safety criterion is adopted as the premise, the 
interconnection relation of a main 
transformer is adopted as the basis, the upper-lower level coordination relation of the power 
distribution system is fully considered, the influence of load transfer limit of medium-
voltage connection and short-time overload of the high-
voltage main 
transformer are considered, and the power supply capability of the power 
distribution system can be accurately estimated, so that the deficiency of the load supply capability 
estimation on quantity when the single 
voltage level is only considered is avoided; the limit of the whole load supply capability of the power distribution 
system can be accurately mastered, so that the planning and the construction of the power distribution 
system is guided; and when the regional load increases in certain degree, the requirement for load increase is met by discovering the power supply capability of the existing power supply facilities. According to the method, the limit utilization ratio of the power distribution equipment can be determined on the premise of meeting the safety of the 
system and reference for a supply transferring scheme can be provided when the equipment fails, thus the 
operation scheduling of the power distribution system is guided and the method is beneficial to the effective use of the power distribution system facilities in power supply enterprises.