Abstract: Taking a 600 MW subcritical boiler as an example, the static and dynamic characteristics of steam temperature were analyzed after low-NO_x retrofit. Results show that great changes have taken place in the boiler after low-NO_x retrofit, such as the in-furnace temperature field, the heating surface slagging and the boiler operation mode, which would significantly affect the steam temperature characteristics. Under high load conditions, the boiler steam temperature is mainly subjected to the combined effects of both furnace outlet gas temperature rise and drop respectively caused by air staging combustion and alleviated heating surface slagging; whereas under low load conditions, the steam tempeature is mainly influenced by the lowered furnace flame center due to air staging combustion and by the outlet oxygen concentration. During unloading process of boiler, the rapid decline of reheat steam temperture is caused by both the lowering of furnace flame center and the dropping of exhaust steam temperature in high-pressure cylinder of steam turbines.