Abstract: Based on the operating characteristics of a MILD coal gasifier, the effects of following parameters on the flow field, the reflux ratio, and the average residence time were numerically studied, such as the nozzle location, nozzle diameter (jet velocity) and coal particle size, etc. Results show that the flow field distribution in a MILD gasifier is mainly affected by the secondary jet location and the air jet velocity, among which the location of secondary jet shows greater influence. Keeping the primary and secondary air jet velocity constant, as the distance between the secondary jet nozzle and the central line of the furnace increases, both the reflux ratio and the particle average residence time would increase firstly and then decrease. With the rise of jet velocity, the reflux ratio increases, while the particle average residence time reduces; whereas with the reduction of mean diameter of pulverized coal, the reflux ratio changes slightly, but the particle average residence time increases significantly.