The invention provides diamine-triphenol hyperbranched polybenzoxaizne and a preparation method thereof. The method comprises the steps of adding a diamine compound, a triphenol compound, paraformaldehyde and an organic solvent into a container, wherein the mass ratio of the diamine compound to the triphenol compound to paraformaldehyde is 3:2:12; and heating to 60-110 DEG C, carrying out thermostatic reaction for 10-75h, carrying out alkali washing on a reaction liquid through a 0.2mol/L NaOH solution and carrying out water washing, rotary evaporation and vacuum drying to obtain diamine-triphenol hyperbranched polybenzoxaizne, wherein the weight-average molecular weight of the product is 6,000-55,000 and the molecular weight distribution index is 1.7-3.5. Diamine-triphenol hyperbranched polybenzoxaizne is synthesized from the triphenol compound and the diamine compound. Due to a plurality of oxazine rings, the curing product is high in crosslinking density and high in molecular weight, has excellent thermal property and mechanical property, can be used for preparing a high-performance structure material and an electronic packaging material, and can be widely applied to the fields of electronics, aviation, machinery manufacturing and etc.