Borehole instability in bedding shale is one of the main factors restricting the success of the deep oil and gas drilling. Due to the anisotropy of the strength, the serious instability problems occurred easily especially in highly-deviated well drilling. According to the Porous medium elastic mechanics theory, the stress state surrounding the highly-deviated well was established, using double coordinate conversion, the concentrate stress distribution on the bedding plane was obtained, the Mohr-coulomb failure criterion was selected both for the bedding plane and rock matrix, the analyze method of borehole stability for highly-deviated well was established, comprehensive considering the attitudes of the bedding plane, well inclination and azimuth, in-situ stress and so on. The results showed that, for the bedding plane with specific attitude, the deviation and azimuth angle has important influence on the borehole stability. When the deviation angle is higher than the specific angle, the collapse pressure rises rapidly, the instability risk increases, the drilling fluid density to keep borehole stability was higher, the collapse pressure of the highly-deviated well towards the direction of maximum horizontal in-situ stress is highest, the instability risk is biggest, the drilling should avoid towards the direction.