Ignition is the key technology of in⁃situ combustion, which is related to the smooth start of in⁃situ combustion. Because the structure of artificial ignition device was complex, there are some risks of pressure fluctuation and casing damage during operation. Based on the working principle of the traditional igniter, a discardable ignition device for oil reservoir is proposed. The basic structure, installation method and construction process of the igniter are designed. The ignition device provides the necessary heat to start in⁃situ combustion by the solid fuel combustion. It is droppable and no need to recover after complete combustion. The device can avoid construction risk while satisfying the requirements of the ignition. A calculation results of the example shows that the device is feasible and can improve the ignition success rate effectively.