Abstract: Uranium material is a very important ingredient of nuclear industry, it is also a very important object in the field of nuclear safeguards. How to accurately determine the mass of uranium in nuclear material is a popular research topic of non-destructive assay. Nowadays, active non-destructive assay is the most usual assay to accurately determine the mass of uranium in nuclear material. Previous active neutron detection assay is the quality of calibration, but this report use a new method of active neutron detection, this report include principle of measurement, method of measurement, the experimental process, data processing and result analyzing. This research explores and validates new method with measuring and analyzing 10 group of uranium samples. From the measurements result, the measurement error is 1.7%, which is within non-destructive error(5%), improve that this method is available. In the process of method establishment, using different abundance uranium samples to confirm the formula to calculate effective mass of ²³⁵U, applicable to the same conditions to rapid non-destructive measurements.