To study the synthesis of 3,4-dihydro-2H-3-phenyl-1,3-benzoxazine（benzoxazine）,the reaction paths of phenol,aniline and formaldehyde were investigated by analyzing the synthesis crude products.With the aid of high-performance liquid chromatography（HPLC）,chromatographic column and preparative HPLC,seven compounds originated from the crude products were obtained and their chemical structures were elucidated.Possible reaction paths are proposed based on these compounds.Results show that Nhydroxymethyl aniline（HMA） derived from the reaction of formaldehyde and aniline is probably the key intermediate during the reaction.HMA can react with itself or other reactants to form other intermediates,such as 1,3,5-triphenyl-1,3,5-triazinane and 2-（（phenylamino）methyl）phenol,and further form benzoxazine and byproducts.
