The invention relates to a cyan compound amidoximation method, belongs to the technical field of preparation of amidoxime materials, and aims to provide a cyan compound amidoximation method which is high in cyan conversion rate. According to the method, hydroxylamine salt solution and cyan compounds react in supercritical fluid to obtain amidoxime materials. According to the method, reaction can be accelerated, reaction time is shortened, and the cyan conversion rate can further be increased. Besides, the method is simple, low in equipment requirement and less in investment, and large-scale industrial production is easily achieved.