With the focus on improving coal burnout and controlling NOx emissions in down-fired boilers, a new deep air-staging combustion technology, the hot air packing technology (HAPT), was investigated by experiments and numerical simulations. The effects of the special secondary air ports added in the furnace ash hopper (SA-H) and the furnace bottom (SA-B) were analyzed by comparing the three cases: the HAPT, no-SA-H, and no-SA-B cases. The experiments with Guizhou anthracite coal in a down-fired 3.5 MW pilot facility showed that the HAPT case presented a good performance of both NO emissions of 683 mg/Nm(3) at O-2 = 6% and coal burnout, 3.07% of unburned coal in fly ash. Simulation results using Fluent software satisfactorily coincided with the experiment results of the HAPT case. It was found by simulation that the HAPT case formed a rational aerodynamic field in the furnace, refrained dead recirculation zones from emerging in the ash hopper, and implemented an air-packed and deep air-staging coal combustion inside the furnace. SA-H flows took the responsibility of destroying dead recirculating zones in the ash hopper, and SB-H flows affected the penetration depth of primary air flow and the utilization rate of the ash hopper.