The invention relates to a pH response insulin slow release nanoparticle, and a preparation method and an application thereof, and concretely discloses a triblock copolymer. The triblock copolymer is an A-B-C block copolymer, wherein the A block is biodegradable polyethylene glycol monomethyl ether, and the molecular weight is 4000-6000; the B block is polycaprolactone, and the molecular weight is 8000-15000; and the C block is N,N-diethylaminoethyl polybasic polymethacrylate, and the molecular weight is 8000-12000. The pH response insulin slow release nanoparticle is formed by a nanocapsule formed by self-assembling the triblock polymer and insulin loaded on the nanocapsule. The nanoparticle can accurately deliver drugs according to different pH values, and can simultaneously reach sustained and controlled release effects.