Abstract: Aimed at the fact that dynamic strata pressure accidents easily occurred during upward section mining of gully terrain at the No.4104 working face of Ch uancaogedan Coal Mine ,the breaking forms of the key strata and strata pressure characteristics during upward mining of the working face under the condition of non-ex isting key strata in gully region were studied.Results indicated that the key strata of the upward section existed as a " cantilever beam" mode under the effect of non-uni formly distributed load because of the lack of gully key strata,which may induce shear damage or tensile damage of the key strata rock mass ,and correspondingly the in stable forms presented as sliding instability or rotary instability which were influenced by the valley slope angle.In the condition of No.4104 working face,overlying key s trata presented as tensile damage and rotary instability failure form when gully slope angle less than 57°,while key strata presented as shear damage and sliding instab ility failure form when gully slope angle more than 57°. Field test showed that dynamic strata pressure behavior was obvious during mining at upward section of gully ter rain of the mining face. Finally,countermeasures to slow down mine pressure behavior and improve roof control effect were proposed.