In this paper, we developed a near-infrared laser sensor for the detection of methane (CH₄) isotope abundance with tunable laser diode absorption spectroscopy for gas detection and analysis applications in petrochemical and other fields. To improve the stability of isotope abundance detection, we adopted a customized pressure control module with two electronic proportional valves to dynamically control the pressure of the gas cell. With the target pressure being set to 13.332 kPa, the average monitoring pressure in 30 min was 13.326 kPa, and the 1σ standard deviation was 25 Pa. To improve the detection accuracy of isotope abundance, we applied a linear regression algorithm instead of the traditional absorbance maximum ratio method. The detection experiment was carried out with 5×10 ^-3 (volume fraction) standard CH₄ gas, and the results of the two methods were compared. The results demonstrate that the average isotope abundance (δ¹³CH₄) obtained by the absorbance maximum ratio method is 1.633%, and the 1σ standard deviation is 0.962%. The results largely deviate from the theoretical values and have poor stability. The 1σ standard deviation obtained by the linear regression algorithm is 0.367%, and the average value is -4.652%, which is consistent with the isotope abundance results of natural CH₄. The stability of the linear regression algorithm detection results is three times that of the maximum ratio method. The pressure control scheme and linear regression algorithm proposed in this article lay a foundation for the development of practical isotope abundance sensors and show potential application prospects in environmental protection, resource exploration, and other fields.