Clinothem slope facies is very advantageous to development of source rock of marine facies in the western margin of Ordos BasinAccording to the element geochemical characteristics，the relationships between element geochemistry and sedimentary environment，and the relationships between the distribution of source rock and heatflow of oceanfloor are discussed in this article by the numbers through analyzing the rules of element concentrate and transference and the change of sedimentary water mass and oxidationreduction condition on the different horizons and the different areasThe conclusion is that water mass depth and reduction and biocoenosis and the heatflow of oceanfloor are very important to the development of source rocksIn the Zhuozishan Formation on the north of the western margin and Sandaogou Formation on the south of the western margin，the preservation of organism is very difficult，because during their deposition，the  water mass was very shallow and widen，and the reduction was weakIn the Kelimoli Formation and Wulalike Formation on the north of western margin and the first section of Pingliang Formation on the south of the western margin，the abundance of organism is very high，because during their deposition the  water mass was very occlusive and the reduction was very strong，also heatflow of the ocean floor was very activeThese analyses provide the basement of element geochemical characteristic for evaluating the reservoir of the gas