Abstract: The loop system for iodine-125 production by China Advanced Research Reactor (CARR) was a set of device which was fully enclosed and long pipe system that made by stainless steel. The system must be strict installation and debugging before installation in the reactor, and it need to leak detection as well to ensure design requirements. According to the requirements of the place of CARR, the designing and debugging simulation system was primarily focused, mainly including the system’s installation, vaccum debugging and Xenon gas recovery test. The methods of subsection debugging for long pipeline and guiding gas test with the pipe system were carried out. After the installation and commissioning of the system, recovery simulation experiment of natural abundance of xenon was also carried out. The results showed that the I-125 simulation loop was a slender and multi bending pipeline. The system had good sealability and the measured value less than 10^-6 Pa•m³/s of leak detection by helium mass-spectrometer leak detector. It took 120 seconds to recover the guiding natural Xenon,which could meet the design requirements. The system scheme was feasible and provided the basis for further iodine-125 production of loop circuit method by reactor.