Abstract: The major causes of low heat efficiency for the high-pressure once-through boiler include high tail smoke temperature, fouling of finned tube of convection bank of tubes and high excess air coefficient. The paper points out that to rationally utilize the fume waste heat, cleani the fouling with ultrasonic method and improve the adjusting mechanism and performance of burner of boiler can effectively improve the heat efficiency for the high-pressure once-through boiler.