The phase holdup of gas-liquid two-phase flow in shale gas horizontal wells is an important parameter for calculating phase separation velocity, pressure drop, average density，and gas production. To solve the problem of gas-liquid two-phase flow phase holdup measurement in shale gas horizontal wells, this paper studies the absorption characteristics of horizontal gas-liquid two phase flow based on near-infrared spectroscopy. Firstly, according to the full-band absorption spectra of methane and water obtained from HITRAN and Refractiveindex databases, the characteristic absorption peak ranges of methane and water are analyzed. Then, the near-infrared spectra of methane and water with different liquid surface thicknesses under different pressures are obtained experimentally. The position and variation range of the absorption peaks are analyzed, and the absorption characteristic wavelengths of methane and water are finally determined to be 1 650 and 980 nm, respectively. Finally, the experimental platform of horizontal tube section with 1 650 and 980 nm wavelength lasers was built to analyze the effects of different pressures, gas-liquid ratios, organic matter and total dissolved solids in the flowback fluid on the near-infrared absorption performance. The experimental results show that the 980 nm near-infrared light intensity is only affected by the liquid level height, and the logarithm of the near-infrared light intensity at the receiving end decreases linearly with the increase of the liquid level height. The near-infrared light intensity at 1 650 nm is affected by the height of the water level and the pressure of the methane gas, and as the height of the liquid level increases and the pressure increases, the logarithm of the near-infrared light intensity at the receiving end decreases linearly. The effect of total dissolved solids in the flowback fluid on the near-infrared light transmittance is slightly greater than that of organic matter. Increasing the concentration of organic matter and total dissolved solids, the effect on the near-infrared light intensity is less than 6%. Therefore, 980 nm near-infrared light can be used to measure the change in water level, and 1 650 nm near-infrared light can be used to measure the change in water and methane pressure. Then, according to Lambert-Beer and linear superposition law, the phase holdup of gas-liquid two-phase flow in shale gas horizontal wells can be obtained.