The invention belongs to the two technical fields such as medical preparations and medical devices, relates to new uses of a water dispersion technology in external application preparations, and discloses a pharmacologically-active chitosan/ethyl cellulose long-acting spraying agent and a preparation method thereof, wherein the components of the pharmacologically-active chitosan/ethyl cellulose long-acting spraying agent in the final solution comprise, by mass volume percentage, 0-5% of chitosan and derivative thereof, 0-10% of ethyl cellulose, 0.1-10% of an emulsifier, 0.1-10% of a plasticizer, 0.1-2% of a defoamer, 0-5% of an acid, a proper amount of a pH value adjusting agent, 0-10% of other non-essential excipients, and the balance of purified water. According to the present invention,the pharmacologically-active true film can be formed after the pharmacologically-active chitosan/ethyl cellulose long-acting spraying agent is sprayed onto the skin so as to achieve the beneficial effects of long acting, water resistance, friction resistance, wound healing promotion, scar formation reduction and spot concealing.