Abstract: The geocell-reinforced structures (GRS) are widely adopted in transportation infrastructure such as highways and railways due to their good seismic performance, simple construction and low cost. At present, in GRS study, only the tensile strength of geocells is considered, the effects of geocell size of geometry are not considered, so the selection of geocells mainly depends on engineering experience. The effects of geocell strip height, junction spacing and normal stress on the shear mechanical characteristics of geocell-reinforced gravel sand are studied by conducting a series of laboratory direct shear tests on five types of geocells. The reinforcement effects of different normal stresses and geocell sizes are evaluated by introducing the reinforced strength coefficient. Finally, the influences of geocell size on shear strength parameters are analyzed. It is determined that the geocell with different sizes can effectively improve the shear strength of reinforced structures, and the shear strength increases with the increase of strip height and the decrease of junction spacing. Meanwhile, the contribution of the strip height to the shear strength is about 1.8 times that of the junction spacing. The shear strength of geocell reinforced gravel sand increases with the increase of normal stress, but its reinforced strength coefficient decreases with the increase of normal stress. Under 50 kPa, the increase of strip height to the reinforced strength coefficient is more than 12.57%, while the increase of junction spacing to the reinforced strength coefficient is less than 3.80%. The geocell reinforcement can significantly improve the cohesion of infill materials, especially the strip height, with an increase of about 25%, the increase of internal friction angle is relatively small, and the maximum increment is 5.11°. The test results can provide an experimental basis for the application of geocells in practical engineering and theoretical researches.