The waste classification has not been carried out worldwide, especially in developing countries. The high content of water in the kitchen waste will definitely affect the amount of air flowing into waste layer from leachate collection pipe. In this experiment, three lab-scale landfill simulation reactors were established. Reactor A and B are semi-aerobic landfill modes, while reactor C has no vertical gas vent. The void fraction in the waste of reactor B was increased by adding gravel serve as part of the waste. The waste sample used in landfill reactor mainly included kitchen waste (58%). The waste decomposition conditions in the landfill were investigated using temperature sensors embedded in the waste, by determining the velocity and gas flow direction and by measuring the volume and composition of leachate produced. The results showed that the void fraction of waste in reactor A and C was 29.79% and 30.86% respectively, and that of waste in reactor B 34.96%. Compared with reactor A, reactor B had its temperature increase earlier. In addition, the temperature distribution in vertical gas vent of the reactor A and B is higher than in the leachate collection pipe. The gas flux of vertical gas vent increased with the temperature of gas vent. Reactor A and B had significantly lower concentration of chemical oxygen demand (COD) and ammonia nitrogen (NH-N) than that of reactor C. It was concluded that landfill decomposition can be accelerated by increasing the void fraction in the waste and keeping a vertical gas vent open.