The invention particularly relates to a stable multilayer-film structural foaming agent and a preparation method of the stable multilayer-film structural foaming agent. The technical scheme is that the preparation method comprises steps as follows: getting 20 to 50wt% of main agent, 20 to 50wt% of assistant and 20 to 50wt% of foam stabilizer as the raw materials at 15 to 25 DEG C; then adding foam stabilizer of which the mass is 10 to 20 times that of the raw materials mentioned above; and agitating for 5 to 15 minutes, so as to obtain the stable multilayer-film structural foaming agent, wherein the main agent is one of sodium lauryl sulfate, sodium dodecyl benzene sulfonate, sodium dodecyl sulfate, alkylphenol ethoxylates and fatty alcohol-polyoxyethylene ether; the assistant is one of dodecanol, polyethylene glycol, setanol, octadecanol and lauromacrogol; and the foam stabilizer is one of sodium carboxymethylcellulose, gelatin, sodium carboxymethyl starch, arabia gum adhesive and hydroxyethyl cellulose. The preparation method has the characteristics of being simple, convenient to operate, and short in preparation time and the like; and the prepared stable multilayer-film structural foaming agent is relatively small in dimension, uniform in distribution, full in foaming and high in stability.