The invention discloses a preparation method of radix physochlainae granules for relieving asthma. The preparation method comprises the following steps of (1) smashing radix physochlainae to form coarse powder, carrying out reflux extraction by using an ethanol water solution to obtain an extracting solution, filtering to obtain filtrate, recovering ethanol from the filtrate, and concentrating to obtain concentrated paste; (2) diluting the concentrated paste with purified water according to the mass ratio of 1:(0.8-1.5), adding ammonia water to alkalize to enable the pH value of the solution to be equal to 8-11 to obtain an alkalized diluent, extracting 2-4 times by using ethyl acetate which is 0.5-3 times as much as the volume of the alkalized diluent to obtain an extracting solution, recovering ethyl acetate, and volatilizing a water bath until no ethyl acetate smell to obtain a radix physochlainae extract; and (3) adding saccharose, starch or dextrin, uniformly mixing, granulating and drying to obtain the radix physochlainae granules for relieving asthma. Experiments prove that the radix physochlainae granules for relieving asthma, prepared by using the preparation method disclosed by the invention, have a favorable asthma relieving effect. The radix physochlainae granules for relieving asthma are high in effect taking speed, convenient to take, remarkable in curative effect and capable of simultaneously treating both symptoms and root causes, so that the requirements of extensive patients can be met. By using the preparation method, few labor hours are needed, and the transfer rate of effective components is high.