The present disclosure provides an siRNA nanocapsule and a preparation method and use thereof, relating to the technical field of biomedical engineering. The siRNA nanocapsule provided in the present disclosure includes siRNA and a shell encapsulating the siRNA and polymerized by a monomer A and a monomer B. The monomer A has a double bond at one end, and is electrostatically bound with the siRNA, and the monomer B includes molecules for improving tumor microenvironment sensitivity. The siRNA nanocapsule provided in the present disclosure is suitable for a wide range of clinical applications.