The organic geochemistry study on the black and red-beds of Cretaceous sediments from Chuangde section of Gyangze in southern Tibet shows that the Organic carbon content of black beds is 5 to 10 times that of red beds, the predominant carbon number of the normal alkane in the black and red bed sediments are nC23 and nC25, respectively; The parent organic matter of both black and red beds was predominantly aquatic plants, and algae and bacteria with minor being terrestrial matter. It is likely that the difference in the predominant carbon number of normal alkane in the black bed and red bed may be indicative to temperature difference during the red bed and black bed sedimentation. It is also suggested that the red bed deposited at a slightly higher temperature than the black bed. Under the high temperature condition, development of marine organism and terrestrial plant were restrained, resulting in the decreasing of reproduction and preservation of original organism during the sedimentation of the red bed.