In this paper, the structural principle of Herriott-type long optical range cell is adopted, and the optimal solution for the number of reflections of the Herriott cell under certain conditions is obtained through theoretical research and simulation analysis, and the design of a long optical range, low-cost and small-volume optical range cell is carried out by utilizing coated concave mirrors as mirrors, and by integrating the optical elements in the cell body. After experimental verification, the designed light-range cell with a physical length of 23 cm and volume of 243 mL of optical range cell can achieve 11 m effective optical range length, and built in the TDLAS methane detection system. The results show that the lower limit of detection is the lowest concentration of 47.6 ppb, which provides an effective way promote the application of the low-concentration, high-precision, and miniaturized TDLAS methane detection system.