The invention provides a modeling method for power system transient state stability assessment. The method includes the following steps that power generator track information and a transient state calculation result are collected; a feature value of a power generator is calculated; an initial mathematic model X and a transient state stability assessment mathematic model F are formed; dimensionality reduction is conducted on the transient state stability assessment mathematic model F to obtain a two-dimensional standard mathematic model D. Multidimensional counting is conducted on power generator track curves, a statistic curve can reflect main mean values, change ranges and change rate features of each track curve, statistic features are irrelevant to the scale of a system, the dimensionality curse problem caused by increasing of an analysis system in the data modeling process can be effectively avoided, and meanwhile adverse of power generator information loss on calculation can be reduced to the largest extent.