Abstract: By submerging GCr15 steel rod in water to simulate rapid cooldown after rolling, the influence of cooling parameters on the ultimate structure and carbide of the steel is investigated. The results suggest that providing the cooling temperature is in a range of 700~500℃, the size and distribution of carbide after quenching are improved as the level of carbide network decreased from 2.0 to 1.0, the level of spheroidite increased from 1.0 to 2.0~2.5. The quenching hardness of sphoroidized samples after rapid cooldown by submerging in water is higher than that of annealing ones after rolling though through the same heat treatment.