To keep coal workers away from the hazardous area with frequent accidents such as the roof fall and rib spalling in an underground coalmine, we put forward the solution with robotized self-moving anchor-supporting unit. The existing research shows that the surrounding rock of the roadway has self-stability, and the early or late support is not conducive to the safe and reliable support of the roadway, so there is a problem of support opportunity. In order to study the supporting effect and the optimal supporting time of the above solution, we established the mechanical coupling model of surrounding rock and advance support, and investigated the surrounding rock deformation and advance support pressure distribution under different reserved roof subsidence by using the numerical simulation software FLAC3D. The results show that the deformation of surrounding rock increases and finally tends to a stable level with the increase of pre settlement of roadway roof, and when the pre settlement of roof is between 8-15mm, the vertical pressure of the top beam of advance support reaches the minimum value, about 0.58MPa. Based on the above research, we put forward the optimum supporting time in roadway excavation, and summarized the evaluation method based on the mechanical coupling model of surrounding rock-advance support.