The invention provides a method and system for determining the operation quality of a power transmission network. The method comprises the steps of: determining the operation quality evaluation indexes of the power transmission network; determining an optimal reference sequence according to the operation index information table of the power transmission network, and performing dimensionless processing on parameter values of all the indexes; determining the maximum difference and the minimum difference between the two poles of the indexes; calculating correlation coefficients of index parameters and the optimal reference sequence, and furthermore, calculating the association degree of an index sequence in each time period and the optimal reference sequence according to the correlation coefficients; and performing comparative sorting on the operation quality according to the association degree, and evaluating the operation quality level. According to the method and system for determiningthe operation quality of the power transmission network provided by the invention, according to operation characteristics and operation and maintenance requirements of the power transmission network,proper quality evaluation indexes are selected; the operation quality of the power transmission network is determined by adoption of a gray system evaluation method of a fussy neural network; and thus, theoretical basis and technical reference are provided for making a reasonable power transmission network operation and maintenance strategy.