Abstract: Along with the world energy demand rising, unconventional energy such as shale gas, tight gas, and CBM, etc. have emerged as the supplement of conventional energy. However, due to specialties of unconventional reservoir, i.e., low porosity, low permeability, easy expansion and fragility, this kind of reservoir can be readily damaged irreversibly during the reservoir development. In order to understand the mechanism of formation damage induced by drilling in unconventional reservoirs, research on the formation damage by shale drilling domestically and internationally was systematically reviewed. In addition, existing problems in the study of formation damage were analyzed and suggestions for next formation protection were given. Based on the analysis, it was found that the study of formation damage by shale drilling is mainly reflected in two aspects, i.e. formation damage induced by drilling technology and drilling fluid. However, there are fewer studies of borehole stability in unconventional reservoirs and lack of deep understanding of the formation damage mechanism induced by drilling fluids. Based on the development of formation damage by shale drilling, the studies of borehole stability in unconventional reservoirs, mechanism of formation damage induced by drilling fluids and the optimization of drilling fluids will be conducted systematically.