The invention discloses a polyamide VOCs (Volatile Organic Chemicals) cutoff type polymer separation membrane and a preparation method thereof and belongs to the field of organic synthesis and membrane separation. The method comprises the following steps: catalyzing a compound A under the action of a phase transfer catalyst quaternary ammonium salt, and oxidizing the compound A to obtain a compound B; carrying out polymerization reaction on the generated compound B and a compound monomer containing amino under the action of an acid binding agent and a catalyst triphenyl phosphite; after reacting, pouring an obtained polymer solution into de-ionized water and precipitating; filtering and drying in vacuum to obtain an oligomer; dissolving the oligomer into an organic polar solvent; carrying out ultrasonic crushing to obtain a membrane solution; coating the membrane solution on a solvent-resistance polysulfone bottom membrane; carrying out cross-linking and drying in vacuum to obtain the triptyl VOCs retention type polymer separation membrane. According to the polyamide VOCs retention type polymer separation membrane prepared by the invention, the polyamide VOCs cutoff type polymer separation membrane can be used for separating nitrogen gas/VOCs. (A formula A and a formula B are shown in the description.).