Preparation of nano chitosan in the invention almost has no chemical reaction, chitosan is mainly dissolved and dispersed, and chitosan is not dissolved in a sodium hydroxide solution, so that chitosan particles are separated out. Meanwhile, preparation conditions are mild, the safety is high, and preparation raw materials are common and nontoxic. The obtained nano chitosan is an ideal raw material for preparing artificial skin, the prepared artificial skin is soft in texture and is comfortable, the laminating performance between the prepared artificial skin and a wound surface is good, and the prepared artificial skin is breathable, can absorb water, has antibacterial and anti-inflammatory effects, and has the functions of stopping pain, arresting bleeding and promoting wound healing. Along with the healing of the wound of a patient and the growth of the skin of the patient, the chitosan artificial skin can be automatically dissolved and absorbed by the body, scraps cannot be left so as to avoid the delay of wound healing, and skin regeneration can be promoted. Moreover, the operation is simple, the safety is improved, and preparation processes are simplified. Required instruments are relatively common so as to be favorable for reducing the cost, and thus the nano chitosan has important application value in the field of artificial skin.