The invention provides a method of semi-continuously producing a particle-size-controllable ADC (azodicarbonamide) foaming agent. Staged reactions are adopted, an oxidizing agent is continuously added, a reaction system is controlled in a certain acidity range, a first stage reaction is continuous, according to the characteristics that true specific gravities of biurea and ADC are the same and particular diameters of the two are different, the particle size of the ADC generated by the reaction is controlled through using a swirl rising liquid flow to perform hierarchical control; and a second stage reaction is a discontinuous reaction, and all reactions are guaranteed to reach endpoint, so that the product quality is guaranteed. The process has the advantages that when the ADC is generated by the reactions, the particle size of the ADC foaming agent can be controlled, and a later crushing process can be reduced, so that an original crystal state is not physically damaged, and meanwhile, the particle size of the product is narrow, and because most reactions are finished in the first stage, batch differences between single kettles are also greatly reduced, and the use stability of the ADC foaming agent is more in favor of being improved.