Underground coal gasification (UCG) is a technique to recover coal energy by the in-situ conversion of coal into gaseous products. In this study, an application of co-axial UCG system with a horizontal well is discussed by means of the model UCG experiment with a large-scale simulated coal seam which the size is 550 × 600 × 2,740 mm. A horizontal well which has 45 mm diameter is used as an injection/production well. The effect of injection rate is evaluated by using the results of gas compositions, temperature profile, and acoustic emission monitoring. During the experiment, the changes of temperature field and product gas compositions were observed by changing the position of an injection pipe, meaning that it is possible to control gasification area and the quality of product gas by controlling the injection position. Additionally, the increase of injection rate attribute to improve the calorific value of product gas while the higher flow rate may cause to move the gasification area rapidly when the coal with higher ash is gasified.