A series of poly(lactic acid)(PLLA 2003D)/TMC-300 composites were prepared by melt blending based on nucleating agent sebacate benzohydydrazide（TMC-300） with the content of 0, 0.1％, 0.2％, 0.3％, 0.5％, respectively. Various techniques including DSC, SEM, polarized optical microscope (POM), heat distortion temperature (HDT) and mechanical property test were employed to investigate the effect of TMC-300 on crystalline property and thermal properties of PLLA 2003D. Experimental results indicate that TMC-300 show significant nucleation effects on PLLA, When the mass fraction of TMC-300 increases from 0 to 0.5％, the crystallinity of PLLA 2003D/TMC-300 composites increases remarkably. When 0.5％ TMC-300 was added, the crystallinity measured by DSC increases from 6.00% to 41.27%; HDT of PLLA 2003D extends to 115.8 ℃ after heat treatment at 110 ℃～120 ℃ for 5min. The tensile strength and notched izod impact strength of the specimens increase with increasing of the mass fraction of TMC. The notched izod impact strength of the PLLA composites containing 0.5％ TMC increases by 49.78%.