The invention discloses a shale reservoir high brittleness optimization method. The method successively includes the following steps: (A) calculating the dynamic Young modulus Ed and the dynamic Poisson's ratio vd of rocks in each section of a reservoir; (B) calculating the I type fracture toughness KIC of the rocks in each section of the reservoir; (C) calculating the brittleness index BI of the rocks in each section of the reservoir by utilizing results of a step (A) and a step (B); and (D) selecting out a layer section with the large brittleness index as a high brittleness layer section. The brittleness of shale reservoir rocks is affected by rock mechanics parameters of a shale and the anti-brittle failure capacity of the shale, the method defines that the brittleness index BI represents the brittleness of the rocks in each section; and a high brittleness shale section can be directly selected out through calculation of the brittleness index BI of the rocks in each section. The method can accurately select out the high brittleness section suitable for fracture in the shale reservoir, and then provides an effective guide for increasing production of the shale reservoir, so that hydraulic fracturing construction in the shale reservoir has pertinence and effectiveness.