Abstract: A numerical calculation method of finite element coupling field was used to simulate the cooling process of big bars. The influential rule of cooling water flow on the cooling effect was obtained by analyzing the numerical result. Moreover, the influence degrees of two factors, the sectional area of the cooler's inlet port and the velocity of cooling water, were compared. The results show that when the cooling water flow is relative small, its change has significantly influence on cooling effect; but when the cooling water flow is relative large, the difference in cooling effect is inappreciable. In addition, the cooling water velocity has a larger influence on cooling effect than the sectional area of the cooler's inlet port.