The invention belongs to the technical field of dyeing of straw-weaved products and particularly relates to a sun-block raffia straw hat dyeing method. The specific method comprises the steps of (1) conducting vapor treatment on weaved raffia straw hats, taking out the raffia straw hats, soaking the raffia straw hats in a dyeing agent, introducing ultrasonic waves to conduct ultrasonic treatment and putting the raffia straw hats into a magnetic field for magnetization treatment; and (2) conducting hot pressing and drying on the raffia straw hats, soaking the raffia straw hats in a sodium alginate aqueous solution, taking out the raffia straw hats and conducting hot pressing and drying on the raffia straw hats. The infiltration capacity of dyeing agent molecules is effectively enhanced. Thepolymerization capacity between the dyeing agent molecules and cellulose is improved. The raffia straw hats are dyed uniformly and thoroughly, are bright in color and extremely stable in dyeing performance, have remarkable anti-ultraviolet performance and cannot discolor after long-time sun exposure or rain drenching. The use quality of the raffia straw hats is effectively improved. The service life of the raffia straw hats is prolonged. Moreover, the anti-corrosion and anti-mildew capacity of the raffia straw hats can be further improved. Breeding of harmful bacteria is inhibited. The raffiastraw hats have not pungent smell and tangy light flower fragrance. The popularity degree of the raffia straw hats is effectively improved.