The invention discloses a continuous firing method of boron-containing SiC fiber. According to the method, SiC fiber is taken as a raw material and is firstly subjected to surface activation treatment, and pretreated fiber with high reaction activity is obtained; the activated fiber is wetted in a solution of a boron-containing compound and dried, and an intermediate fiber is obtained; finally, the intermediate fiber is fired at the high temperature, and the boron-containing SiC fiber is obtained. By means of the provided method, boron can be introduced into a firing furnace in a dynamic quantitative manner, the concentration of boron-containing atmosphere in the firing furnace is kept relatively constant, the boron-containing compound and high-activity SiC fiber subjected to surface activation treatment are subjected to an in-situ reaction, introduction of boron is realized, and the method adopts a simple process and is low in cost and suitable for industrial production. The preparedboron-containing SiC fiber has excellent high-temperature resistance and has good application prospects in aerospace, aviation and high-performance weapons.