Using an IFA300 constant temperature anemometer system, cold air experiments on a quarter-scaled burner model sited in a 300 MWe down-fired boiler were conducted to investigate the influence of various inner secondary air vane angles on the flow characteristics in the burner nozzle region. By increasing vane angles, no central recirculation zone appeared, the axial velocity decay rate increased, radial velocities increased at the jet boundary, and tangential velocities clearly increased in the inner secondary air zone. Industrial experiments were also performed on a down-fired pulverized-coal 300 MWe utility boiler with swirl burners. Gas temperature, concentrations of gas components (O-2, CO, and NOx) in the burning region, and carbon content in the fly ash were measured with inner secondary air vane angles of 42 degrees, 47 degrees, 53 degrees, and 60 degrees. By increasing vane angles up to 53 degrees, NOx emission and boiler efficiency increased; when vane angles were increased to 60 degrees, NOx emission increased, but boiler efficiency decreased.