Cooling down the high temperature of blanking rapidly is a key problem in hot stamping procedure. Two different cooling tunnels were set in hot stamping mold, one was smooth inner wall, and another added triangle backup bars in it. Cooling performance for blanking in the two cases as well as the flow and heat transfer situation of cooling water in two different tunnels were obtained after the numerical simulation. The result shows that, the cooling effect of inner backup bars tunnel is advantageous than smooth tunnel, and also the heat transfer ability is stronger. For backup bars tunnel, the average temperature of work piece is 12k lower than that of smooth tunnel while holding time is 10 s. For designing of cooling tunnels in hot stamping, this research also provided important references.