Increasing absorbance by lengthening the absorption path is a direct and effective approach to improve the signal-to-noise ratio of infrared gas absorption spectroscopy. However, once the absorption path is extended by designing and optimizing the gas cell structure to a certain extent, a bottleneck will appear due to the difficulties in the optical alignment and the interference effect. A modified tunable diode laser absorption spectroscopy system with a dual fiber loop configuration is proposed that can extend the effective absorption path length of the original multipass cell several times. The relevant theoretical model has been established and its effectiveness has been verified through experiments.