The online rapid detection technology of warhead length and weight by rotor type was researched for improve efficiency and precision of detection of the small-bore bullet slug’s warhead. And a system of online rapid detection for warhead length and weight was desired on the basis. The structure of the system and the principle of online length and weight detection were introduced on the paper. The beat and accuracy of the on-line detection and sort system based on some key technology were researched, such as technology of high speed feeding, technology of rapid detection by rotor type and technology of towards by spiral. The results of test by prototype show: The beats of length and weight on-line detection for small-bore bullet slug by system of online rapid detection for warhead’s length and weight can reach 240/minute, the precision of length detection is 5×10-6 m, and the accuracy of weight detection is 0.01g under the beat. The detection efficiency and detection accuracy of small-bore bullet warhead on-line detection have improved much by the system, and it is a technological breakthrough in cartridge detection. It has practical significance for improvement of quality and efficiency of cartridges production.