This paper introduces in detail the whole process of resin replacement of heavy water purification system in a reactor reconstruction project in Algeria, including old resin discharge, pipeline cleaning, new resin filling, new resin deuterization, water quality detection, heavy water storage and continuous operation of the system. By sorting out deuterization data and tracking and analyzing the water quality detection results, it is considered that the resin deuterization process of the heavy water purification system of a reactor is smooth. After deuterization, the effluent concentrations of the three resin columns of the heavy water purification system meet the operation requirements. The whole deuterization process tries to save precious high concentration heavy water for Algeria. After deuterization, the resin column is connected to the heavy water purification system. After continuous operation and sampling detection, it is determined that the purification effect is ideal and the pH value is not affected. The resin of the heavy water purification system is successfully replaced and can be put into use. At the same time, aiming at some problems in the deuterization process, this paper analyzes the causes in detail, summarizes the experience and lessons, and gives optimization suggestions and precautions in the deuterization process.