A method of welding structural steel containing, by mass%, Cr: 1.5 to 3.5%, Mo: 0.5 to 1.5%, and V: 0.15 to 0.5%. It comprises preheating joint of the structural steel to be welded at temperatures of 150 to 250 degrees Celsius; multilayer welding the joint end portions; keeping the interpass temperature of the joint end portions during the multilayer welding at 150 to 350 degrees Celsius; then after welding completion, performing DHT by heat treating the weld zone before cooling down below 150 degrees Celsius under the conditions that the temperature is 250 to 340 degrees Celsius and that the treatment time is 5 to 10 hours.