Abstract: In view of the fact that most of the existing chemo-mechanical coupling analysis of the wellbore stability in shale gas horizontal wellsonly considered the influence of hydration on rock strength, but rarely considered the influence of hydration strain and stress, this paper, based on the theories of elasticity and rock mechanics, and by considering the weakening effect of hydration on rock mechanical parameters and the additional hydration stress, established the prediction model of wellbore collapse pressure of bedded shale gas horizontal wells under chemo-mechanical coupling, studied the mechanism of wellbore instability of bedded shale gas horizontal wells, and analyzed the factors affecting wellbore stability and their influencing laws. The results showed that when there was a bedding plane, the collapse pressure would increase greatly; the wellbore stability was the best when drilling along the bedding plane; when the hydration time was fixed, the collapse pressure would decrease with the increase of the radial distance from the wellbore, and the longer the hydration time was, the larger the area near the wellbore that was prone to collapse would be; and after considering the influence of the hydration stress, the collapse pressure increased greatly, sothe influence of hydration stress could not be ignored when designing the drilling fluid density. The research results enriched the wellbore instability theories of shale gas horizontal wells, and played a guiding role in the drilling design of bedded shale gas horizontal wells.