Abstract: Objective: To utilize the method of low-does CT to reduce the exposure to X-ray,to reduce the radiation to the human body,to carry out the screening on primary asymptomatic lung cancer,to increases the screening rate,to realize the early diagnosis and treatment against disease and to increase the survival rate.It improves the situation that has been for a long time,in which the lung cancer attacks unnoticeably and is difficulty to be diagnosed.Method: To divide 500 cases having no symptom in the chest into two groups: smoking group and non-smoking group.Aided by employing the HRCT & Image Post-processing Technology in the local lesion,low-does scanning parameter was applied in increasing the screening rate of primary lung cancer.Result: 35 cases were confirmed to be carrying tubercle out of 500 cases,among which 6 cases were confirmed as lung cancer;7 cases as benign lesion(2 cases as hamartoma,2 cases as tuberculoma and 3 cases as inflammatory masses) while the remaining 22 cases were confirmed as negative tubercle.Besides,87 cases were confirmed as other types of lung disease(emphysema,bulla of lung,inflammation,obsolete tuberculosis,hydrothorax,pachynsis pleurae,etc.) and 378 cases are normal.The 6 lung cancer cases were given surgery,radiotherapy,chemotherapy,etc.respectively.Conclusion: The low-does CT,which can increase the screening rate and realize the early diagnosis and treatment against disease,is an effective method to detect primary asymptomatic lung cancer.