Thermal analysis is an effective mean to study the crystallization of polymers. Fast scanning chip calorimetry (FSC) has ultra-high cooling and heating rate and plays an important role in the study of crystallization behavior. The crystallization kinetics of poly (l-lactic acid) (PLLA) with amino polyhedral oligomeric silsesquioxane (POSS-NH₂) and polyethylene glycol-grafted POSS (POSS-PEG) was investigated by traditional differential scanning calorimetry (DSC) and FSC. The results show that the addition of POSS-PEG has a better promoting effect on the crystallization rate of PLLA than POSS-NH₂. And there are two differences between the results of FSC and DSC: firstly, FSC can effectively avoid the nucleation and crystallization behavior in the cooling process and ensure that the crystallization process occurs completely in the isothermal stage, while DSC cannot; second, the measured crystallization rate by FSC is lower than the traditional DSC data. In a word, POSS plays a role of nucleation agent in PLLA crystallization, and PEG as nucleation accelerator further improves the crystallization rate; FSC can effectively avoid the nucleation and crystallization in the cooling and heating process.