The invention discloses a preparation method of organic silicon modified waterborne UV curable polyurethane (PU) with high poly-alkenyl activity. The method comprises the following reactions: I. firstly subjecting polyether or polyester polyol, hydroxy-terminated silicone oil and a diisocyanate trimer to reaction to obtain a hydroxy-terminated solution; II. reacting DMPA with aromatic or aliphatic diisocyanate to obtain a -NCO-blocked solution, then dropwise adding the reactant I to the reactant II to obtain an organic silicon modified prepolymer subjected to chain extension, and then carrying out blocking reaction on the organic silicon modified prepolymer subjected to chain extension by using hydroxyethyl methylacrylate, hydroxyethyl acrylate or pentaerythritol triacrylate, thus obtaining an organic silicon modified PU prepolymer; and finally carrying out neutralization reaction on a system by using a triethylamine neutralizer, adding water for dilution and carrying out stirring and emulsification, thus obtaining the organic silicon modified waterborne UV curable PU emulsion. A UV curable film has better water resistance, hardness and adhesion and can be used for environmental protection, buildings, household appliances, and the like.