Gasification is a potential technology to convert municipal solid waste into energy in the form of syngas. Addition of air to the pyrolysis zone and oxidation was carried out by modifying a single-stage downdraft gasifier into a multistage air inlet. The results showed an increase in the syngas heating value and decreased tar content. To determine the performance, the effects of equivalent ratio, preheated air temperature, and air ratio were studied. When the equivalent ratio is increased, the flammable gas and LHV decrease. The optimum conditions were obtained for the equivalent ratio (ER) of 0.4, where the percentage of CO and H-2 increased at an oxidation temperature of 902 degrees C. The variation of the air ratio has a stronger influence than the effect of the equivalent ratio because at the same equivalent ratio an increase in pyrolysis temperature of 674 degrees C is favorable to reforming tar from primary tar to secondary tar. The CO percentage increased significantly from 18.17% to 22.51%. Air preheating is useful to improve gasification performance, which was characterized by an increase in LHV from 5254 to 5976 kJ/kg. The optimum equivalent ratio and air ratio were 0.4 and 40:60, respectively, and effectively reduced the tar content from 50.02 to 27.82 mg/Nm(3). The results of this study can be used to optimize multistage gasifier performance using air preheating and a multistage air inlet.