The invention relates to a method and device for continuously producing a bio-based environment-friendly flame-retardant plasticizer. The method has the characteristic of process simplicity, and the device has the characteristics of low equipment requirements, easiness for maintenance and running stability. According to the technical solution, the method for continuously producing the bio-based environment-friendly flame-retardant plasticizer sequentially comprises the following steps: (1) preforming light-catalyzed reaction on unsaturated methyl ester, methanol and chlorine; (2) introducing chlorine into a reacted material for reaction; (3) performing gas deacidification on a material discharged from a second reaction column to obtain a finished product. The device for continuously producing the bio-based environment-friendly flame-retardant plasticizer comprises a first reaction column, a back pressure valve and the second reaction column, wherein a light source is mounted in an inner cavity of the first reaction column, and an unsaturated methyl ester inlet, a methanol inlet, a first chlorine inlet and a material outlet are formed in the reaction column; a material inlet, a second chlorine inlet, a tail gas outlet and a product outlet are formed in the second reaction column.