The work aims to improve interphase compatibility of the PLA blend system toughened by vegetable oil polyol and L-lysine ethyl ester diisocyanate (LDI) as biobased monomers via in-situ polymerization. In the process of toughening PLA by the above 2 monomers via in-situ polymerization, a small amount of dicumyl peroxide (DCP) was incorporated to initiate reactive compatibilization between the in-situformed crosslinked polyurethane toughening phase and PLA matrix. Then, the effects of DCP on microstructure, mechanical properties, and crystallization/melting properties of the prepared PLA blend system were investigated, respectively. The addition of DCP resulted in not only an increase in gel content of polyurethane as a toughening phase, but also an improvement in interfacial compatibility. When the weight content of DCP was 0.8%, the notched impact strength for PLA blend system reached the highest value (12.3 kJ/m2) that was 4.4 times that of neat PLA. Besides, with an increase in the amount of DCP from 0 to 1.2%, both melting peak temperature and crystallinity associated with PLA component in the blend system decreased gradually from 163.8 ℃ and 7.3% to 155.6 ℃ and 3.2%, respectively. Therefore, a kind of full biobased PLA material with good toughness can be obtained by incorporating a small amount of DCP into the PLA system toughened with biobased monomers via the in-situ polymerization approach.