Blend of polyethylene terephthalate (PET) with SiO2 and poly terephthalate (PCTG) is a way for improving comprehensive characteristics of PET. Investigation of the variation law of the thermal behavior of the blended material may provide theoretical basis for the blending technology of PET/ PCTG /SiO2. By determination of the temperature increase and decrease differential scanning calorimetry (DSC) curves of the blends containing PET, PCTG and SiO2 with different particle sizes, the effects of the particle size and dosage of SiO2 and PCTG on the cold and hot crystallinity of PET/ PCTG /SiO2 blend were studied. In the PET/ PCTG /SiO2 blend, the addition of PCTG and SiO2 would reduce the cold crystallization temperature and increase the hot crystallization temperature. The higher the SiO2 dosage, the lower the cold crystallization temperature and the higher the hot crystallization temperature of PET/PCTG/SiO2 blends. PCTG and SiO2 had relatively large synergic effect on the cold and hot crystallization temperature, whereas the grain size of SiO2 had relatively small effect on the cold crystallization temperature and relatively large effect on the hot crystallization temperature. The smaller the grain size of SiO2, the higher the hot crystallization temperature.