The invention relates to a foam drainage gas recovery method used for a natural gas horizontal well. The method is capable of injecting a foam scrubbing agent into the bottommost end of a gas well shaft, so that the whole shaft is filled with foam fluid and optimal drainage gas recovery effect is achieved. The technical scheme of the method comprises the following steps: firstly, manufacturing a dynamical underground foam scrubbing bar which consists of a gas nozzle, a tail wing, a boosting agent, a shell and a protection head sleeve, wherein the material for manufacturing the tail wing, the shell and the protection head sleeve is the solid foam scrubbing agent which consists of polyoxyethylene alkyl ethers, polyethylene glycol, urea, imidazoline, sodium dodecyl benzene sulfonate and saturated alcohol sulfate; and the boosting agent is one of dry ice, sodium hydride or potassium oxide; and secondly, throwing the dynamical underground foam scrubbing bar to the bottom of the well, wherein the boosting agent is in contact with water to generate a large amount of gas, so that the foam scrubbing bar is pushed to the bottommost end; and as the foam scrubbing agent is dissolved, a large amount of foam is formed to achieve the optimal effect of drainage gas recovery. The method disclosed by the invention has a wide application range without any wellhead equipment and energy, is simpleand safe in operation, low in cost and has no pollution to the environment.