Objective：To investigate the correlations between CT scan parameters and noises of different tissues and to discuss the factors influencing the image quality. Methods：The anthropomorphic phantom equivalent to human tissue was scanned by 16 slices spiral scanner（GE BrightSpeed） with different voltages（80，100，120 kV and 140 kV），tube currents（80，100，120，180，240 mA and 300 mA） and pitches（0.562，0.938，1.375 and 1.75）. 120 kV，300 mA and 0.938（pitch） were using as the standard. One of the three scanning parameters was changed and other scanning parameters were fixed. The CT value and image noise were recorded and an－alyzed（Standard derivation，SD）. Results：There was no statistical difference in noises of the lung among groups of 80，100，120，140 kV（F=0.966，P ＞0.05）. There were statistical differences between groups of 80 kV and 120 kV in noises of the chest wall，soft tissue of spine and aorta，P＜0.05. The noises of different tissues were statistically different among groups of 80，100，120，180，240 mA and 300 mA（Lung F=3.28，P＜0.05；soft tissue of spine F=11.89，P＜0.05；aorta F=196.67，P＜0.05）. There were statistical differences be－tween 80 mA group and 300 mA group in noises of the lung，chest wall，soft tissue of spine and aorta，P＜0.05. The noises of the lung，soft tissues of chest wall and spine were not statistically different among groups with different pitches（0.562，0.938，1.35 and 1.75）. （Lung F=0.23，P ＞0.05；chest wall F=1.53，P ＞0.05；soft tissue of spine F=2.27，P ＞0.05）. There were statistical differences in noises of aorta among groups with different pitches，F=9.68，P＜0.05. Conclusions：The noises of different tissues are increasing with the de－crease of tube voltage，tube current and increase of pitch，but the increase of noise in the lung is not obviously. The chest scan with low dose can reduce the radiation dose and keep the image quality without obviously increasing the noise in the lung.