<p>To investigate the effect of shear rate on the crack development, the fracture surface morphology and the permeability characteristics of sandstone during direct shear, direct shear tests were conducted on red sandstone at four shear rates of 0.1, 0.5, 1, and 2&#xa0;mm·min⁻¹. Real-time monitoring of acoustic emission (AE) signals and permeability was performed on the sandstone during the entire shearing process. After the tests, a 3D scanner was used to scan the fracture surfaces. The test results showed that during the shearing process, the samples produced more tensile crack AE signals than shear crack AE signals, and with the increase in shear rate, the proportion of shear crack AE signals increased. At low shear rates, the shear-to-compression ratio (SCR) of the samples was relatively high, easily producing intergranular cracks, which was conducive to the formation of fracture surfaces with high roughness. The increase in shear rate promoted the shear slip of the samples, inducing more transgranular cracks, which was conducive to the formation of fracture surfaces with low roughness. Meanwhile, high shear rates intensified pore pressure fluctuations on the shear plane, further exacerbating sample damage and enhancing the connectivity of seepage paths during shearing, thereby improving the flow conductivity of the samples. After failure, fracture surfaces with low roughness exhibited higher seepage capacity.</p>