Thermoset resins have wide applications in coatings, adhesives, and structural components, but often their usage is often limited by their intrinsic brittleness. Here, we report that a thiourea based polymer blending with a kind of thermoset resin (benzoxazine) yields materials improve toughness without deteriorating other properties. Synchronous enhancement in the toughness properties, flexural properties and thermal properties (T_g) is showed in blends containing 5 wt% thiourea based polymer. Notably, there is more than 156%, 35% and 14 °C improvements in the above properties respectively compared with those of polybenzoxazine. A curing mechanism, chemical structure, phase morphology and processing properties of blends are discussed. The results illustrate the modified and newly introduced hydrogen-bonded pairs in the system are the main reason for simultaneously enhancing the properties of cured products. The method by modifying the hydrogen bonds type and amount of thermoset resin is facile to get enhanced comprehensive properties and have a profound meaning for fiber-reinforced composite.