Based on the self-stable phenomena of surrounding rock deformation and failure in the soft rock roadway, the numerical simulation method is adopted to reveal the relationships among the roof, two ribs and floor of the roadway. It is found that the unstable zone of roadway surrounding rock is ellipse around roadway. According to the Protodyakonov’s theory and the interactions among the roof, two ribs and floor, a new theory of self-stable ring is put forward and its elliptic curve equation is given. This research clearly confirms that the rock mass within the ring is the supporting subject and the main purpose of support is to control the stability of rock mass within the ring. This research shows that the “floor - two ribs – roof” constitute the overall system of roadway stability system. The size of self-stable arch in the roadway roof increases with the increase of the plastic zone of ribs, while the plastic zone of ribs increases with the deformation of floor. Hence, the height of ring in the roof will be greatly reduced by strengthening the floor and two ribs. Therefore, the roadway control principle is put forward which can be described as “control roof must control ribs first, and control ribs must control floor first”, and it has been verified in practice by years. This theory provides a new basis for soft rock roadway control.