The invention provides a novel synthetic method of a bis-benzoxazine 
ketone ultraviolet absorbent, and belongs to the technical field of 
fine chemical engineering. The method comprises the following steps: A, stirring, anhydrides, used as raw materials, of o-
aminobenzoic acid and (o-, m-, p-) phthaloyl dichloride or (o-, m-, p-)
phthalic acid for a certain time in a non-polar 
solvent; B, adding chemical dehydrating agent or physical dehydrating agent in a 
reaction system without separating, slowly heating and refluxing for a certain time to obtain (o-, m-, p-)substituted bis-benzoxazine 
ketone ultraviolet absorbent; wherein the stirring time in the step A is not less than 1 hour, the refluxing time is 5-10 hours in the step B, the chemical dehydrating agent used in the step B is various dehydrating agents reacted with the water, including but not limited to alkaline 
calcium oxide, 
soda lime, acidic concentrated 
sulfuric acid, concentrated 
phosphoric acid, polyphosphoric acid, 
phosphorus pentoxide, 
thionyl chloride, 
acetic anhydride and the like, neutral 
molecular sieve, water-absorbent, 
anhydrous cupric 
sulfate and the like; the physical dehydrating agent comprises but not limited to non-protonic 
solvent such as 
benzene, methylbenzene, 
xylene and the like. The method provided by the invention has the advantages of being simple in operation flow, low in cost, simple in equipment, and suitable for the scale industrial production.