The coal gasification on earth surface causes the high cost of transportation and environmental pollution, and yet the in-situ coal gasification in underground is difficult to be controlled. In light of these problems, author advances the idea that the main equipments such as gasification boiler are installed in underground to construct underground coal gasification plant at a mine, the caved coal is gasified in the underground gasification plant, and produced coal gas is transported to surface in pipe. This paper makes a rough approach to the feasibility and possible problems about the idea.