Unconventional oil and gas reservoirs typically require fracturing to achieve industrial capacity. Logging evaluation for rock brittleness is one of the important factors that should be considered in the design of fracturing for unconventional oil and gas reservoirs. At home and abroad, the brittleness index is defined variably and calculated by different methods. However, there is a lack of a complete research method flow for brittleness index evaluation with logging data. This paper reviews the history of the oil and gas reservoir brittleness index, provides a scientific evaluation of brittleness index definitions and summarizes brittleness index calculation methods. Finally, the Chang 7 tight oil reservoir in Ordos Basin is taken as an example for discussing the calculation processes and effectiveness of logging evaluation methods for brittleness index. When there are comprehensive wave and shear wave logging data, the rock brittleness index can be calculated directly by Poisson’s ratio and Young’s modulus method or by using mineral composition which could be gained from either Elemental Capture Spectroscopy (ECS) logging curves or optimization method based on conventional logging data. X-ray diffraction data and regression of GR/Pe can also be used to establish an empirical formula for the brittleness index which is suitable for the target study layers to achieve logging evaluation of the brittleness index. Finally, the problems existing in the brittleness index evaluation with logging data are discussed, and the future development direction is put forward. The research results can provide scientific guidance for drilling and fracturing layer optimization of unconventional oil and gas reservoirs.