Abstract: The traditional method for determining the strips'density variation ratio(DVR) in case is a manual and destructive operation,and unable to correct excessive DVR in case during tobacco processing.Therefore,an online automatic detection and control system was developed,a strips DVR detector was applied to detect the DVR of packed strips,the densities,DVRs and standard deviations at 9 test points were determined.By comparing the average density in the transversal direction and longitudinal direction with the average density of the 9 test points separately to calculate the density deviation,the automatic control of strips DVR was realized by adjusting the angle of strips spreading plate in the transversal direction and the stroke of the cylinder driving the spreading plates in the longitudinal direction through a PID control system.The results of application showed that the control system reduced the strips DVR in case obviously,the proportion of strips with DVR ≤ 10 accounted for 91.4%,while that of strips with DVR15 only for 0.45%.