The invention relates to a modified nylon 66 resin, a preparation method and application thereof. According to the invention, during preparation, aliphatic dibasic acid, aromatic polyamine, and/or tetramethylpiperidine and the like are added so as to obtain the modified nylon 66 resin. The aliphatic dibasic acid, aromatic polyamine, and/or tetramethylpiperidine are used as modifying agents during polymerization. The modifying agents can obviously improve the spinning stability of the modified nylon 66 resin provided by the invention, so that the melt spinning process can be smoother and more stable, and the spinning process is easier to control. The nylon 66 filament obtained by melt spinning of the modified nylon 66 resin has a filament number of 0.2-1.0dtex, and is a fine denier and superfine denier fiber.