Body surface exposure to X-ray radiation was measured in those with synthetic clue investigation on tuberculosis. The results showed body surface exposure in them appeared a logarithmic normal distribution with a geometric mean of 0.19 mC/kg and was higher than that with fluoroscopy in routine check-ups. The late effect of X-ray radiation showed 0.52 hours of an average life-span cut. But, based on prevalence, mortality and cure rate of chemotherapy for tuberculosis in Jiangsu Province, chest fluoroscopy in synthetic clue investigations brought an average prolongation of 45.8 hours per person in life-span of those X-rayed. Comparison of life-span showed synthetic clue investigation was an adequate method in active tuberculosis case-finding from the viewpoint of radiation protection.