The present invention relates to a transient stability assessment input characteristic validity analysis method based on improved Sammon mapping. The method comprises removing redundant data in power grid operation sample data by using a fuzzy C-means clustering algorithm; obtaining three-dimensional data having the maximum contribution rate in the power grid operation sample data by using a principal component analysis method as initial values of a low-dimensional space mapping point coordinate vector of the power grid operation sample data; correcting the initial values of the low-dimensional space mapping point coordinate vector of the power grid operation sample data by using an iteration correction method, and obtaining the low-dimensional space mapping point coordinate vector of the power grid operation sample data; and judging validity of the power grid operation sample data according to the low-dimensional space mapping point coordinate vector of the power grid operation sample data. According to the method, when transient stability assessment is performed on a power system, the initial values are provided for iteration by using the principal component analysis method to stabilize a mapping result, low-dimensional space mapping point coordinates are solved by using the iteration correction method, and the solving speed is accelerated.