Abstract: By preparing graphene oxide (GO) concrete, the effects of GO platelets with different sizes on the mechanical properties of concrete materials were systematically studied. GO-concrete samples with different particle sizes (D50: 1,3.8,6.8 and 10.8 μm) and contents were prepared, and their effects on the mechanical properties and microstructure of the samples were systematically analyzed. The results show that GO of all particle sizes can improve the compressive strength of concrete, and the enhancement effect depends on the synergistic effect of dosage and particle size, and the optimal dosage decreases with the increase of particle size. In the range of test dosage, the highest compressive strength of the concrete corresponding to the four sizes was 59.9 MPa, 58.7 MPa, 56.7 MPa and 58.9 MPa, respectively, 20.77%, 18.35%, 14.31% and 18.75% higher than that of the control sample. The microstructure analysis shows that the incorporation of GO makes the cement matrix more dense, and it is found that the particle size has a regulatory effect on the morphology of hydration products. Combined with the analysis of ImageJ image processing results, GO promotes local densification by adsorbing Ca²⁺, and acts as a physical barrier to deflect, bifurcate or even block microcracks, thereby delaying crack propagation and increasing energy consumption. XRD and TG analysis further verify that the larger particle size GO can promote the hydration reaction and optimize the composition of hydration products. The comprehensive results show that GO effectively improves the compressive strength of concrete through the synergistic mechanism of ' physical crack resistance ' and ' chemical coagulation '.