Hollow fiber has been successfully used in infrared wavelength regions for energy delivery and gas sensing. Metallic hollow fiber is used in spectroscopic sensing system for colored solutions owing to its low-loss property in visible light regions. A stable and practical sensing system is established for detecting the concentration of colored solutions based on spectroscopic absorption. The system sensing characterizations are analysed by theoretical analysis and computational simulation. Experiments on measuring the concentration of CoCl2 water solution are conducted. The experimental results show that the system has the advantages of rapid response, easy operation and high sensitivity. The possibilities of miniaturization and on-line measurement make the system a potential candidate for promising applications in the environment monitoring, chemical process control and medicine fabrication processing etc.