Objective This paper studies on feasibility of low dose CT scanning in lung cancer patients simulated localisation. Methods 62 patients cases of lung cancer are selected. Scan parameter:scan twice by 20/100 mA, the other parameter remain unchanged as voltage of 120 kV, thickness of 5 mm, pitch of 1∶1 and scan time of 1 s. After scan, picture quality was evaluated according to excellent, good, bad under different condition. Volume of target was determined by treatment planning system. Data such as dose index value of single helical scan, z-axis scan range, dose length product value and etc. are recorded in order to evaluate radiation dose of patients. Picture quality and the difference of radiation dose were statistically analyzed using Fisher′s and pair t-test. Results Picture quality of low dose scanning was a little bit lower than that of normal dose, however, picture quality difference of difference dose scanning was statistically meaningless (number of patients according to excellent, good, bad were 46,13, 3 and 50,11,1,P=0.541). There is no obvious difference of target volume under different dose scanning in the same (36.78 cm³,40.35 cm³,t=2.57,P=0.189).Radiation dose of low dose scanning group is far less than that of high dose scanning group and the difference is obvious (133.05 mGy,941.25 mGy,t=－41.24,P=0.000). Conclusions Low dose scanning of 20 mA current during CT simulated localisation tremendously reduces harm that may happen to patients during CT scan, while tumor target delineation and scanned picture quality is guaranteed