The article studies influence of laboratory-simulated external influencing operational factors – water and moisture saturation, combined effect of elevated temperature and humidity, exposure in a tropical climate chamber on the properties of high-temperature carbon fiber based on a melted thermosetting polyimide binder. Studies of the structure, glass transition temperature and elastic-strength characteristics of carbon fiber after exposure were carried out, the change in the mass of carbon fiber samples during long-term exposure to water and moisture was estimated.