The invention provides an underground coal gasification ignition device and an ignition method thereof. The underground coal gasification ignition device comprises a conveying pipe. The conveying pipe is used for being arranged in a well-cementing casing pipe of a gas inlet drill hole, a first end of the conveying pipe is connected with the ground surface, a second end of the conveying pipe is suspended in a coal bed, and the conveying pipe is used for conveying self-igniting gas to the coal bed; a gap between the conveying pipe and the well-cementing casing pipe forms an annular space, a first end of the annular space is closed, a second end of the annular space is open and corresponds to the coal bed, a gas input port is formed in the first end of the annular space, and the gas input port is used for conveying combustion-supporting gas into the annular space; and the second end of the annular space is used for conveying the combustion-supporting gas into the coal bed, and the self-igniting gas is used for self-igniting to ignite the coal bed after being mixed with the combustion-supporting gas. According to the underground coal gasification ignition device and the ignition method thereof, the coal bed can be more conveniently and rapidly ignited, implementation is easy, so that coal bed combustion is convenient to control, ignition of the coal bed can be accurately ensured, and the underground coal gasification ignition device and the ignition method thereof are particularly suitable for a non-well underground gasification furnace.