Abstract: The effect of antimony on the microstructure and mechanical properties of high-strength gray cast iron sections with different thicknesses was studied by casting step test block, optical microscope and hardness test.The results show that when the antimony content of gray cast iron is 0.02%, the graphite flakes are moderately refined, the volume fraction of pearlite is increased and the content is above 98%, but no white surfaces appear, and the average hardness is also obviously improved.With the increase of thickness, the size, quantity and morphology of graphite structure remain basically unchanged, and the matrix structure also maintains uniformity, while the hardness decreases significantly slower, which greatly improves the sectional sensitivity of high-strength gray cast iron castings.