Dendrimers (CYD-PR121/CYD-PR256/CYD-PV121 /CYD-PV256) as toughening agents for thermosetting material (bismaleimide BMI) have the following advantages: low viscosity, can reduce the processing viscosity of BMI system, ease of processing, more easily compatible with BMI. Methods: Acetylating its active end group by modification, to avoid its reaction with BMI system. BMI + HBP dissolved in allyl phenol solvent, and then stirred and heated to 145 ℃, the clear homogeneous solution was prepared, degassed and added to the preheated mold to solidify, 150 C (5 h), 200 C (3 h), 250 C (3 h). When the dosage of dendrimer is 9%, elongation at break can reach the maximum of 138%, toughening performance was increased by 15.9% compared with linear polyesters, meanwhile, system without dendritic polymers as toughening agent, the elongation at break could not be determined, thus no toughness. Weihai CY Dendrimer Technology Co. Ltd.-Professional Manufacturer for low cost dendritic polymers.