Abstract: From the perspective of macroscopic and microscopic points, the paper studies the influences of gelled acid used during fracturing on the mechanical properties of the Ordovician carbonate rocks in the Block Shunbei of Tahe oilfield, which could provide basis for efficient development of the carbonate reservoirs in the target blocks. The experiments were carried out to test the influences on microscopic structures and its mechanical properties of carbonate rock samples after treatment by gelled acid and the results showed that the mineral components of the Ordovician carbonate rocks in Shunbei area are characterized by high contents of carbonate minerals, low content of quartz and a few impurities; after the static acid-rock reaction, the intercrystal distance of minerals significantly increases and the calcite content reduces from 93% to 88%, indicating a high-brittleness fracturable reservoir; the static acid-rock reactions in different acid fluids and the corresponding uniaxial compression tests show that the optimal reaction time is 30 minutes, and each physical parameter and mechanics index get worse obviously; the density and P-wave velocity decrease obviously after 30 minutes of gelled acid treatment for the rock samples and the tensile and shear strengths significantly drop; the gelled acid as a reaction acid fluid can result in acid etching to the macrostructures and some damages to micropores of the carbonate rock samples. Therefore, the gelled acid is of great significance for carbonate reservoir fracturing and fracture propagation