The exploitation of deep oil and gas resources has become an important strategy of national oil and gas development， and borehole instability in mudstone and shale formations is the technical bottleneck restricting the safe and efficient development of deep oil and gas resources. This paper analyzes the mechanical and chemical mechanisms of deep mudstone shale borehole failure with the focus on the research status and development trend of wellbore stability prediction models for shale hydration， weak structural plane， anisotropy and multi-field coupling. Improper mud density is the major cause for mechanical wellbore failure， while mudstone and shale hydrations are the major causes for chemical wellbore failure. Investigation of the effects of the weak plane and anisotropy on the safe density window of drilling mud is the major method to study the wellbore stability in deep mud and shale formations under the action of the fluid-solid-chemical-thermal coupling behavior on the wellbore.