Kilograms of polytrimethylene terephthalate (PTT)with different molecular weight was synthesized by direct melt condensation in a 5 L stainless steel reactor, using terephthalic acid and biological 1,3-propylene glycol as raw materials and tetrabutyl titanate as catalyst. The synthesized PTT was identified by 1H-NMR. The viscosity average molecular weight was calculated from the intrinsic viscosity by Ubbelohde viscometer, and its value is (4.7~6.3)×104. The crystallization and melting behavior as function of molecular weight were investigated by differential scanning calorimetry (DSC), XRD and polarizing microscope (POM). The results demonstrate that the crystallinity and crystallization rate decrease with the increase of molecular weight, while the equilibrium melting point increases with the increase of molecular weight, reaching the equilibrium when the molecular weight is higher than 5.5427×104. Rheological tests show that the increase of molecular weight improves the elasticity and decreases the viscosity of the material. The mechanical properties test shows that the secondary yield phenomenon occurs in all samples under uniaxial tension. The yield strength is increased with the increase of molecular weight, while the elongation at break increases first and then decreases. This work is important for the acquisition of excellent performance biological PTT polyester with practical value.