The developments of clean and renewable energy sources are needed in order to reduce dependency of fossil fuel and global warming. Wood pellet is one of clean renewable energy sources and has been considered as one of the substitutes for fossil fuels. Wood combustion is a complex process. It involves many physical and chemical processes. Burning phases of wood pellet can be classified into three modes, 1) gasification mode, 2) flame burning mode and 3) charcoal burning mode. The test equipment used moving grate combustor. Primary air is supplied from the bottom of the grate and the flame is formed above moving grate. case 1) moving grate is organized as horizontal stairs. As increases the number of grate combustion occurs in a lot of unnecessary space. Case 2) the grate was adjusted angle In order to minimize the space below. case1), there was a flame until 8 stairs. The temperature inside the chamber was 1100℃. In case of case2 was a flame until 4 stairs and The temperature inside the chamber was 1200℃. Although the combustion chamber temperature slight increase, the flame length was shorter.