Long-wave infrared spectrum (8~14 μm) is important electromagnetic radiation between middle infrared and terahertz wave, corresponding to the spectral radiation band of the target object at room temperature on the earth surface and the “Third Atmospheric Window” of the earth. Compared with short-wave and medium-wave spectral radiation, long-wave infrared radiation is less affected by atmospheric scattering. Therefore, the long-wave infrared photodetector is widely used in infrared spectral imaging, infrared reconnaissance, spectral detection and other fields. So the absolute spectral responsivity, as one of the main parameters to characterize the response ability of detectors, needs to be solved urgently for its high-precision calibration. At present, the traditional calibration method based on the standard radiation source can no longer meet the requirements of high precision absolute spectral responsivity. At present, there is no long-wave infrared absolute spectral responsivity calibration device based on laser source and cryogenic radiometer in China. The main reason is the lack of laser source with stable power, high beam quality, and long-wave infrared standard transfer detector with stable performance. In order to measure the absolute spectral responsivity of detectors with high accuracy, we are reporting a laser-based absolute spectral responsivity calibration device in the long-wave infrared spectral range. The tunable CO₂ stable frequency laser was selected as the light source, and the cryogenic radiometer was used as the light power measurement benchmark. CdTe crystal electro-optic modulator is used to construct the laser power stability control system. Based on the beam transmission theory, a long wave infrared spatial filter is constructed to optimize the beam quality. A standard transfer detector with stable and reliable performance was developed by integrating/sphere HgCdTe detector, and a calibration device with high absolute spectral response rate and high accuracy of long-wave infrared detector was established. We measured the HgCdTe/sphere detectors at 9.62 and 10.60 μm, respectively. The experimental results show that the extended uncertainty of optical power measurement was less than 0.30%~0.42%(k=2) by using cryogenic radiometer; The extended uncertainty of the absolute spectral responsivity measurement has been analyzed to be 0.80%~1.02% (k=2), other wavelengths can be referenced for analysis. The work realizes the high accuracy calibration of absolute spectral responsivity of long wave infrared detector based on laser source.