The thermal dilation experiment and the martensite transformation features of modified high Cr ferritic heat-resistant steel upon continuous cooling were explored at various cooling rates. The “spread” martensite transformation model was introduced to investigate the influence of the cooling rate applied on the martensite transformation behaviors. The martensite fraction, martensite formation rate, and the density of martensite laths were obtained as a function of cooling rate. Both the onset and offset temperatures of the martensite transformation decrease with the increase of cooling rate, and the martensite formation rate bursts at the beginning of transformation and then reaches a peak rapidly. The fitted data based on the proposed kinetic model indicated that the aspect ratio of martensite lath decreases, instead the density of martensite laths increases, with the increase of cooling rate.