Abstract: Objective to investigate the effect of different trigger threshold on image enhancement in chest CT. Methods the chest CT enhancement scan patients in our hospital were divided into 3 groups, and the threshold of scan trigger was set to 120HU in group A, 21 patients. 160HU was set as the threshold in group B, with 26 patients. The threshold of group C was set in 21 patients with 200HU. Smart trigger technique was used in the first arterial phase and the second venous phase was delayed by 45s in all enrolled patients. CT values of descending aorta at pulmonary artery level and venous stage were measured. Results the weight of patients in the 3 groups was (66.38±9.08)kg in group A, (67.46±8.56) kg in group B, and (66.38±6.66) kg in group C. Arterial CT value of group A (296.86±36.76)HU, group B (321.62±40.18)HU, and group C (318.11±42.21)HU, P=0.009, P<0.05 were statistically significant; venous CT value of group A (158.67±15.96)HU, group B (168.35±14.69)HU, and group C (171.62±12.851)HU, P=0.014, P<0.05 were statistically significant. Objective image quality score of group A, group B and group C was 4.90 greater than that of group B, 4.69 greater than that of group A, 4.47. Conclusion the statistical analysis of the three groups all met the clinical diagnostic requirements, and the filling effect of the arterial and venous phases was better in group C, which was conducive to the differential diagnosis of pulmonary diseases between radiologists and clinicians.