Abstract: Coal reburning is a successful advanced technology for reducing NOx emissions from utility coal-fired boilers. In this work, various rank coals were employed as reburning fuel, the effects of reburning fuel ratio, reacting zone temperature, excess air, residual time and coal fineness on NOx reduction efficiency were experimentally investigated by using an one-dimension drop-tube furnace. The experimental results show that the coal with high volatile content can reduce NOx more effectively. For the same coal, in order to achieve high NOx reduction efficiency, the finer coal finess and suitable residence time of the reburning zone are required. The minimum burn-out height has been put forward to evaluate the right location of the reburning coal injection ports to get a higher carbon burn-out and higher NOx reduction efficiency.