Deep reservoirs with abundant oil and gas resources are difficult to exploit safely and efficiently due to complex geological conditions and engineering factors. The problems of stuck drilling， well collapse， and well leakage caused by unstable wellbore walls have led to huge losses to drilling engineering. Therefore， this paper analyzes the mechanical mechanism of unstable wellbore walls and focuses on the influence mechanism of mechanics and multi-field coupling on unstable wellbore walls. Finally， it proposes suggestions for promoting the theoretical and technical development of drilling in weak side of deep stratified formations. The study found that the development of weak side， high temperature and high pressure environment， changes in rock layer inclination， and hydration of rocks are the main factors that weaken the mechanical strength of rocks and cause instability of the wellbore walls in deep reservoirs. The mechanical strength of rocks under different inclinations is significantly different， and the weak side of stratified rocks is more likely to swell due to hydration， which requires the rational optimization of drilling engineering parameters and drilling fluid density. This paper systematically summarizes the research on the rock mechanics and related aspects， deeply understands the mechanical influence mechanism of wellbore wall stability in deep reservoirs， and provides reference for actual production and engineering practice.