Abstract: In order to promote the efficiency and accuracy for detecting capsule in filter rod, a detector was designed based on microwave resonance cavity perturbation technique. The detector was mainly composed of a filter rod feeding device, a filter rod conveying device, a microwave detection unit and a sorting device. The capsule missing, position and defects of capsule, in filter rod could be detected quickly via an established wave crest shape and position recognition algorithm. The results showed that the designed detector and the established algorithm featured higher accuracy for detecting the position of capsule and good recognition effect for defects or absence of capsule. The maximum standard deviation was 0.111 mm in the capsule position repeatability test, and the accuracy of capsule defect detection reached 100% at a rate of 120 rods per minute. The detector provides a rapid and accurate quality detection method for capsuled-filter rods.