At present，the railway entered a rapid development period. The traction rectifier is one of the core components of EMU，in which effective cooling can increase the security of the locomotive，so studying the traction converter cooling system is very meaningful. By building a wind tunnel test bench， the heat transfer characteristics of plate-fin heat pipe radiator are experimentally investigated when air inlet temperature is at 25-45 ℃ and air speed is at 5-7 m/s，which include heat dissipation，substrate temperature range and main factors affecting the heat transfer. The results show that the substrate working temperature of radiator is normally at 70-90 ℃; the heat dissipation increases with the increase of substrate temperature; the effect of inlet air temperature on heat dissipation is greater than that of air speed.