Abstract: The rib spalling is a technical problem to be solved urgently in steeply dipping thick seam mining. Based on the geological conditions and characteristics of strata behaviors at No. 25221 working face in 2130 Coal Mine,the load and instability characteristics of coal wall is investigated by theoretical analysis,numerical simulation,physical ana- logue material simulation,and field monitoring. Results show that the asymmetry characteristics of mining pressure and strata behavior of large mining height face is higher than that of general mining height face in steeply dipping seam, which is due to mining height increase. Because the inhomogeneous characteristics of the overburden filling are further enhanced,the asymmetric characteristics of the supporting pressure of the coal wall are also obviously increased. Dur- ing the process of mining,the mechanical properties of coal wall will gradually deteriorate,coal wall crazes and slip body appears. Then the slip body slides along the slip surface,rib spalling emerges,when the surrounding constraints of slip body are relieved or support pressure increases. In inclination direction,the central area is the high incidence area of rib spalling,upper secondary and lower minimum,which is consistent with the asymmetric loading characteristics of coal wall. Besides,in vertical direction,the displacement at the upper part of coal wall is larger than that at the lower part,and rib spalling is easy to occur near the roof area. And under the influence of the gravity tendency component of coal wall,the rib spalling is easy to spread to the upside. On the basis of safety production demands at No. 25221 working face in 2130 Coal Mine,some control measures have been proposed in the paper.