Abstract: Objective: To use the technique of active breathing control (ABC) for treatment of non-small cell lung cancer (NSCLC), to evaluate the effect of respiratory movement on mobility of the pulmonary tumor, and to examine the predominance and feasibility of ABC technology, as well as the short term curative effect and acute radioreaction. Methods: Nine advanced NSCLC patients were chosen to be treated with the ABC method and three-dimensional conformal radiotherapy (3D-CRT). Each patient received computed tomography (CT) scans under two respiration conditions: free breath (FB) and active breath-hold. The effect of respiratory movement on mobility of the lung tumor was evaluated, and planning target volume (PTV) margin and dose-volume histograms (DVH) were also examined. A dose of 54-60 GY/18-20 fractions, 3 GY/fraction, 1 f/d and 5 d/w was used and the short-term effect was evaluated. The adverse effects of radiotherapy were also evaluated during the treatment. Results: With use of the ABC, the boundary picture of the pulmonary diaphragm at free breath (FB) was observed to be 24.5 mm (20.0-32.0 mm) to 3.64 mm (0.5-7.2 mm), and the lung-chestwall boundary was observed to be 3.2 mm (2.8-4 mm) to 1.2 mm (0.5-1.6 mm). PTV margin can then be reduced from 1.5 cm to 0.75 cm. The V20 was lowered from 21.8% to 15.0% when using ABC, and on average V20 were reduced 30.6%. The short-term effects include 6 CR and 3 PR. Acute toxicity is mild. Conclusion: In the precise radiotherapy of lung cancer, the influence of breathing can not be ignored. The ABC system reduced the influence of breathing, improved the precision of the radiotherapy and reduced the toxicity.But it is also rather complex, it prolongs the treatment time, and some patients can not tolerate the treatment.