Abstract: To overcome the shortcoming of low sensitivity in RIM-FOS with LED coupling with multimode fiber as illumination purpose, the intensity modulation model was built and experiment system was designed using LD coupling with single mode fiber as illumination and multimode fiber as receiving purpose. The experiment system was made up of LD module, optic module, PIN detection module, signal collection module, FPGA module, up computer system and power module. The validation of model was proved by experiment results and the performance of RIM-FOS resulting a sensitivity of 3.15 mV/m and linear range of 380 m for front slope, a sensitivity of 0.76 mV/m and linear range of 690 m for back slope was presented. Good stability and repetition was also proved by experimental results, and the experiment system would play a significant effect for the further study of RIM-FOS with single mode illumination.