Abstract: In order to meet the need of in-line determination of advanced two-cycle reprocessing process, an in-line determination instrument for plutonium in 1BP was designed, processed and installed according to the specific conditions of the reprocessing active test bench and the hot cell. The in-line determination instrument was mainly composed of a detection system, an optical circuit system, a sample circulation pool system and a control and data processing system. The control and data processing program was developed in C language, and wireless module was used to realize wireless signal transmission and remote control and data processing between instrument and computer. The method of the in-line analysis of plutonium in 1BP solution was established by adopting the Pu standard solution calibration instrument. The linear range of the working curve is 0.1 to 5.0 g/L, R²=0.999. Pu standard solution of 0.5 g/L was measured by the in-line determination instrument. The results show that the instrument standard deviation of the results is 0.67%. The results of the thermal experimental application of the in-line determination instrument show that the running status of the process can be determined in real time, and the determination results can be used to guide the adjustment of each phase liquid flow ratio.