Using conventional micronucleus and cytokinesis-block micronucleus of micro-blood, for the subjects of roentgenography upper gastrointestinal once the changes of micronucleus were observed before exposure and 24 h, 1,4 and 9 months after exposure. The results showed that micronucleus of subjects were exposure to a average absorbed doses of two parts for 5.29 cGy, it was raised 24 h after exposure but reduced at 1 month and 4 months or 9 months reached the same level with before exposure. Then, the low dose effects and roentgenography interval were discussed.