For the high cost of production，maintenance and measurement of the correctness gauge which was difficult to meet the needs of the growing test ammunition in the range，a new correctness detection system for conjoint ammunition was designed. Using high precision laser instrument to measure the diameter and center coordinates of the ammunition，the parameters on the 2D vertical section containing the maximum offset of the center coordinates was collected and the coaxial was calculated，then the mathematical model of correctness gauge was established. The result of correctness detection was judged by comparing the 2D profile. The measurement theory and errors was analyzed，and the practical results show that the system could detect correctness for multiple caliber ammunition due to its high accuracy，secure and reliable， accurate result and high efficiency. It has a great value on practice in charging and assembling in the range.