The invention relates to an inverse synthetic aperture radar imaging data segment selecting method. In the method, image contrast is taken as a standard of evaluating image focusing degree, and the optimal imaging data segment selecting method can be simply expressed by a mathematical expression (topt, delta topt)=arg[max(IC)], wherein the topt is the central time of the optimal imaging data segment; the delta topt is the length of the optimal imaging data segment; and the IC is the image contrast; the key for determining the optimal data segment is to calculate the topt and the delta topt from the expression; and the method comprises the following four steps of: 1, generating an ISAR image sequence; 2, calculating image sequence contrast; 3, estimating the central time topt of the optimal data segment; and 4, estimating the length delta topt of the optimal data segment. Images with high resolution and good focusing can be generated according to the optimal data segment.