For study the fluorine and arsenic content and pollution route of the grain in “coalburning ”endemic fluorosis area in Yunnan—Guizhou area and the effect of improved oven for defluorination(OD) in preventing coalburning chronic fluorosis and the situation of OD use in fluorosis areas in Yunnan—Guizhou Provinces, the living habits, the way of drying and preservation for grain and the children's dental fluorosis rate about 500 families were investigated in the famous serious fluorosis areas〖CD2〗Zhenxiong, Weixin, Daguan, Yiliang County and Zhaoyang of Zhaotong City in Yunnan Province and Weining County and Bijie County in Guizhou Province,and non fluorosis areas 〖CD2〗Qiaojia, Ludian County of Zhaotong City in Yunnan Province during Apr. 2005 to Dec. 2008. The fluorine content of grain before and after dried in both using and no using OD areas were analyzed .The results show: the fluorine and arsenic content in most fresh grain are lower or a little more over the state standard, the fluorine content in most fresh corn between 1~2μg/g and arsenic content is lower than 0.1μg/g, general in 0.01 to 0.05μg/g, both in the fluorosis area or no infect area. But after about 10 days dried by burning coal quickly, the fluorine and arsenic content in the dried corn have a great deal increase, fluorine pollution level of grain dried by burning coal quickly.In the area of using OD or not, the fluorine pollution level of grain dried by burning coal quickly and dental fluorosis rate of local people are near same, in both areas are very high, and both of fluorine pollution level of grain dried by burning coal are over state standard, and arsenic pollution level increase more than 10 times than the fresh corn; In the using or nonusing OD districts, dental fluorosis rate of children, who are mainly feed by dried corn by burning coal quickly, come to 100%, and their fluorosis rate are equivalent. The reason of that OD can't decrease the coalburning endemic fluorosis rate of southwest China is not the lower using rate or incorrect use of OD. The reason is its lower firepower which can't dry grain quickly in a short time. So, the main route of fluorine and arsenic pollution of grain in “coalburning” in southwest China endemic fluorosis area is the way of using the open oven burning coal to dry the grain. In the using or nonusing OD districts, people still use the open oven to dry the grain; no one uses the OD to dry the grain.So, it is not enough to improve oven only for defluorination in preventing “coalburning endemic fluorosis” in southwestern China, it can not cut off the source of fluorine when grain dried by burning coal, and need add the other way to together to cut off the source of fluorine.