Casing failures have been frequently encountered during multi-stage hydraulic fracturing of horizontal wells drilled in unconventional reservoirs, resulting in failure to install bridge plugs of subsequent stages to the design depths, or even abandonment of all the remaining fracturing stages. In this paper, we performed an integrated study of casing failures during the fracturing of four horizontal wells drilled in a tight-oil reservoir in Northwest China, by analyzing the field data as well as numerically investigating the influence of various factors on the casing deformation. The results show that: (1) fracturing induced casing failures in this reservoir feature excessive localized radial deformation, and the reduction of diameter generally amounts to 1~3 cm; (2) fracturing-induced non-uniform loading on the casing together with a poor cement sheath may lead to localized yielding, while the reduction of diameter is small, generally not more than 3 mm; (3) asymmetric distribution of the stimulated reservoir volume with respect to the wellbore can cause overall bending deformation of the casing, however, the cross-sectional shape and size does not change noticeably; (4) the high contrast between the two in-situ horizontal principal stresses in this reservoir makes shear activation of pre-existing fractures or faults during the fracturing highly possible, which can deform the casing severely if the pre-existing fracture or fault intersect the casing, resulting in a reduction of diameter larger than 1 cm. By comparison of modeling-obtained deformation magnitude with the field-data, it is concluded that casing impairment during the hydraulic fracturing in this tight-oil reservoir is mainly due to the slip of pre-existing fractures/faults activated during the fracturing. Insights obtained in this study can be helpful for mitigating casing impairments during future fracturing jobs in similar unconventional reservoirs.