poly(D-lactic acid) (PDLA) with different polyethylene glycol (PEG) segment synthesized PDLA-PEG-PDLA triblock copolymer through the ring-opening reaction of D-LA and PEG will be used as a toughening modifier. The microstructure, crystal structures and crystallization behaviors of this triblock copolymer were investigated by fourier transform infrared (ftiR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, X-ray diffraction (XRD), differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The triblock copolymer is synthesized from the appearance of cH 2 stretching vibration peak at 2910 cm −1 and CO stretching vibration peak at 1200 cm −1 from PEG in FTIR spectra. Moreover, the chemical shift that is about 3.6 ppm in 1 H NMR and 68.8ppm in 13 c nMR proves this matter. The results of XRD and DSC reveal that PDLA and PEG are crystallized separately, and are not fully compatible, and microphase separation has occurred in this triblock copolymer. PEG can induce the triblock copolymer to accelerate the rate of crystallization, allowing it to crystallize more completely in the same amount of time. When the molecular weight of PEG is 6000 or the ratio of D-LA/ PEG is 1/1, the crystallizability of PDLA-PEG-PDLA triblock copolymer is the best. The rapid development of industry has brought great convenience to people's lives, but the environmental pollution caused by the rapid development is also gradually exposed, coupled with the oil crisis caused by the extensive development and utilization of petroleum resources, the necessity and urgency of the research and development of degradable polymers are gradually highlighted. Among the various degradable polymers, polylactic acid (PLA) is the most promising as a green polymer material 1-3. The biggest and most prominent advantage of PLA is that it can be recycled in nature 4. Its raw materials are renewable biological resources, so it is no longer dependent on petroleum and other resources. Its wastes are completely transformed into carbon dioxide and water through hydrolysis and a series of biological metabolism, which is harmless to human body and non-toxic, and has no pollution to the environment 5,6. According to the chiral property of the structural unit, PLA can be divided into poly (L-lactic acid) (PLLA), poly (D-lactic acid) (PDLA) and poly (D , L-lactic acid) (PDLLA) 7. However, compared with polyesters with higher rigidity, PLA is a semi-crystalline polymer, which usually has a slower crystallization rate without external force and produces some amorphous products during processing 8,9. And its heat resistance is poor, which limits its application requirements in bioengineering, food packaging and other industries 10-12. Currently, in order to improve its physical or thermodynamic properties, PLA is modified by adding other substances to form composites (such as rice husk hydrochar 13 , lignin 14 , polycarbonate 15 , chitosan 16 , etc.) and polymerizing with other substances (such as PLA-PCVL-PLA 17 , SEBS-g-PLA 18 , etc.). Of course...