Air lift reverse circulation drilling has obvious advantages for lost formation. But through the comparison of positive and reverse circulation drilling processes at several sites, it is found that there is the obvious weakness of easy breakage of drilling tools in reverse circulation compared with direct circulation. In order to guide drilling operations, give full play to the advantages of reverse circulation and eliminate the weakness of reverse circulation, the stress of drilling tools in the hole is analyzed with summarization of the causes for easy breakage of drilling tools in reverse circulation drilling. Subsequent drilling has verified that breakage of drilling tools were effectively reduce.