Roadside filling body in traditional gob-side entry retaining (GER) has several shortcomings such as the insufficient support resistance, the inability to adapt to the deformation of surrounding rock and isolate the goaf effectively. Taking the GER with double roadways by filling with 1.8-m-wide high-water material in gently inclined coal seam of Zuozegou mine as a project case, the mechanical model of GER with double roadways in the gently inclined coal seam is constructed, and the reasonable width of the filling body of GER is verified by combining with the peak strength of high-water material. The FLAC3D numerical simulation method is used to study the distribution characteristics of stress and plastic zone of GER after being affected by the mining disturbance, and the failure range of surrounding rock of GER with double roadways is obtained. Based on this, a coupling control technology named anchor cables and bolts in the roof and solid coal + single props in entry-in support and goaf side of the outer roadway + anchor bolts in roadside high-water material + short anchor cables below the filling body is proposed and conducted in industrial test. Through the coupling methods of arranging borehole peeping and observing the convergences of surrounding rock, the stability of GER with double roadways is analyzed. The results show that GER with double roadways by filling with 1.8-m-wide high-water material has good control effect. The above research has played an active role in promoting the application of high-water material in roadside filling of GER.