The wavelength modulation-active laser heterodyne spectroscopy (WM-ALHS), which introduces wavelength modulation technique into active laser heterodyne spectroscopy, is reported to enhance the gas standoff detection capability of weak return optical power. The ALHS gas standoff detection system is developed using a 1.65 μm butterfly packaged distributed feedback laser with tail fiber and an all-fiber structure, which successfully detects methane concentrations at a distance of 35 cm using an aluminum plate as the reflective surface. Allan variance analysis shows that the system has good stability, and the detection limit at 29.2 s integration time is 0.84 ppm m. Standoff detection experiments with direct absorption-active laser heterodyne spectroscopy (DA-ALHS) and wavelength modulation spectroscopy (WMS) are carried out on the basis of the WM-ALHS system and the detection limits of 4.49 and 1.64 ppm m were achieved within integration times of 18.6 and 29 s for DA-ALHS and WMS, respectively. The superiority of the WM-ALHS method compared to these two spectral detection methods is demonstrated. Furthermore, the feasibility of applying WM-ALHS to gas standoff detection has been verified, laying the foundation for the development of this spectroscopic technology.