During oil and gas well drilling, when the drilling fluid density is too high, not only tensile fracturing but also shear fracturing may occur on the wellbore. The possible fracturing modes and corresponding calculation formulas of fracturing pressure were present. Moreover, the influence of the magnitude and non-uniformity of in-situ stress, the pore pressure and the formation strength on fracturing mode was quantitatively analyzed. The results showed that: the risk of shear fracturing was higher with small non-uniformity of in-situ stress; when the horizontal stress was small, shear fracturing and tensile fracturing both probably happened and a higher in-situ stress leaded to less probability of tensile fracturing; the potential of tensile fracturing increased with the increasing of formation strength and pore pressure.