Abstract: The development of natural gas hydrate has attracted great attention from all over the world. Japan, China and some other countries have successfully implemented the trial production at sea, which further confirmed the resource potential and development feasibility of gas hydrate. However, the monitoring methods for gas composition in production well are far from perfect up to date, which restricts the production process evaluation and risk prediction. Based on the principles of TDLAS, a set of gas composition sensing and monitoring system for methane and carbon dioxide is designed, and the miniaturization and anti-interference improvement are realized according to the gas hydrate production well conditions. It is verified that the developed optical fiber gas composition monitoring instrument is effective and stable for measurement of CH₄ with concentration above 50×10⁻⁶ and CO₂ with concentration above 100×10⁻⁶.