Abstract: In order to overcome the problem of rib spalling at a full-mechanized mining face with large mining height in hard and thick coal seam,the effect of stress path in the process of rib spalling was analyzed based on the practice of 7. 0 m mining height in Hongliulin Mine,China. The process of hard coal seam rib spalling were divided into tensile cracking damage and sliding instability. The rib spalling of tensile cracking-sliding mechanical model for hard and thick coal seam was established,which acquired the relationship between the rib cracking damage depth,width and coal mass strength,mining height,and the critical protecting force of hydraulic support. The structural features and me- chanical property of two type hydraulic support protecting board were analyzed. The results show that the coal mass tensile cracking damage is a necessary,but not sufficient,condition for rib spalling,whether the rib spalling will finally occur depending on whether the cracking damage body will slide instability under the action of hydraulic support and mine pressure. It was hard for hydraulic support to stop the coal mass tensile cracking,but which can guard against the cracking damage body sliding instability. The hydraulic support protecting board adopts the design with telescopic girder and face guard separately,which has the remarkable advantages of bigger supporting force for rib,higher structural strength,and higher reliability.