Abstract: To obtain the detection sensitivity of negative pressure and detectable defect range of the cigarette inspection system in PASSIM cigarette maker, the relationship between the pressure at the filter end of cigarette and the area of defective hole on cigarette surface was analyzed with Computational Fluid Dynamics (CFD). By means of on-site measurement, 3-D modelling, boundary condition simplifying and parameter setting, the vacuum values at the detection points on cigarettes with simulated defective holes of different sizes were computed with Star CCM+. The results showed that:1) When the area of a defective hole was less than that of a circle with the diameter of 0.5 mm, the defective cigarette was undetectable because minute pressure change at the sensor end. 2) When the area of a defective hole was larger than that of a circle with the diameter of 3 mm, the defective cigarette was easy to be detected because the vacuum value at the sensor end was close to that of the negative pressure circumstance. 3) When the area of defective hole ranged from the area of a circle with the diameter of 0.5 mm to that of 3 mm, the detected vacuum value approximately linearly increased with the increase of defective area. The computed results could provide theoretical references for negative pressure detecting system designing, negative pressure adjusting and rejecting limit setting of online cigarette inspection system.