Abstract: Under the influence of open-pit mine stripping and internal backfill,there is a significant difference between the roof structure,overburden rock activity law and mining press show rule in longwall mining face of open-pit slope mine,which is different from the conventional formation condition working face. Therefore,calculation method of roof pressure also needs to be studied theoretically and experimentally according to the special roof overburden structure characteristics and stress field environment of the open-pit mine slope coal. The west side slope and south side slope coal seam in heidaigou open pit No. 1 mining area is research background. The characteristics of the side slope coal seam roof overburden structure are analyzed. The coal seam at the low open-pit bench is internal backfill,and the strip- ping is more. This thinner and lower strength bedrock roof is covered with massive loose dumping. There is essentially no key stratum in the roof of the thick loose overburden of the weak thin bedrock. The weak thin bedrock under the bench of open-pit mine only provides a limited protective effect as immediate roof of longwall mining face. The crush- ing of weak the thin bedrock is also more serious because of the thick loose dumping loading. According to the tradi- tional underground pressure theory,the roof pressure calculation of the thick loose overburden of the weak thin bedrock with no key stratum should be calculated according to the weight of all rock stratum above the support. However,ac- cording to the experimental results of similar materials,the actual pressure of the support is much smaller than the weight of the rock stratum above it. Experiments show that some protective structures still exist in roof strata with no key stratum. Based on the experimental observation and the analysis of underground pressure theory,combined with drawing theory,a hybrid model of the thick loose overburden of weak thin bedrock is proposed. The model is composed of the ellipsoid arch structure and the self-stability of immediate roof. In the open-pit mine slope coal,there are also another with no internal backfill roof overburden types of thin bedrock without overburden. For this roof overburden type,a hybrid model of thin bedrock without overburden is proposed. The model is composed of step cantilever beam structure and the self-stability of immediate roof. This paper summarizes the types of three roof overburden in the open- pit slope coal,and deduces and establishes an analytical formula for calculation method of roof pressure under the con- dition of three roof structures in longwall mining face of open-pit slope mine. According to the hybrid model of the thick loose overburden of weak thin bedrock,that is,the roof pressure calculated by the hybrid mechanical model com- bining ellipsoid arch structure and the self-stability of immediate roof is consistent with the result of similar materials experiment. Considering the self-stability of immediate roof of the calculation of the roof pressure than the traditional do not consider the self-stability of immediate roof of the roof pressure is about 14% less. Using experimental and theoreti- cal analysis methods,the problem of ground pressure,such as roof caving,overburden strata movement,roof pressure calculation and so on,is systematically studied in longwall mining face mining process of open-pit slope mine.