Abstract: The fluorescence photoelectric monitoring is an important method for monitoring groundwater seepage. The value of distortion coefficient is the key to single-hole fluorescence photoelectric monitoring. This paper aims to systematically study the distortion coefficient with different seepage conditions. It designs a test apparatus of seepage monitoring system to monitor the groundwater seepage. First, the mathematical expression of the distortion coefficient for the fluorescence photoelectric method is derived on the basis of the single-hole dilution model. According to homemade photoelectric monitoring device, a test apparatus of seepage monitoring system is then designed to monitor the groundwater seepage. Finally, the variation law of distortion coefficient is studied with different permeability velocity values, single-hole aperture and opening rate. The experimental results show that the distortion coefficient increases with the aquifer and opening rate, but decreases with the aperture of single-hole. What's more, the importance of the influencing factor follows the regulation of the aquifer > the single-hole aperture > the opening rate. The above research results provide a useful reference for the engineering application of single-hole fluorescence photoelectric method in monitoring groundwater seepage.