Polylactic acid (PLA) is a high-modulus, high-strength biodegradable thermoplastic polyester used in the packaging, textile and medical industries. Conventional plasticizers are usually non-biodegradable, the study used low molecular polyhexanediol succinate (PHS) blended with poly (L-lactic acid) (PLLA) to obtain a fully degradable system. The compatibility, crystallization and mechanical properties of the blended system were investigated by differential scanning calorimetry, polarizing microscope and universal testing machine. The results show that the crystallinity of PLLA/PHS ratios of 100/0, 95/5, 90/10, 85/15, and 80/20 were 7.5%, 8.7%, 11.5%, 14.1%, and 14.2%, respectively. The crystallinity of the blends increased with increasing PHS content, indicating that PHS successfully promoted PLLA crystallization. In addition, the crystallization rate of 80/20 was increased 10-fold and the semi-crystallization time was halved compared to pure PLLA. The elongation at break of the blends increased from less than 10% for pure PLLA to about 60% (PHS content 20%), with a slight decrease in strength and modulus. The elastic modulus of the blends decreased continuously with the increase of the PHS content, from 2.25 GPa for pure PLLA to 1.86 GPa at 20% PHS content.