Kilograms of polytrimethylene terephthalate (PTT)with different molecular weight was synthesized by direct melt condensation in a 5L stainless steel reactor, which used 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 was between 47000 and 63000g/mol. The crystallization and melting behavior as function of molecular weight were investigated by Differential Scanning Calorimetry (DSC), XRD and polarizing microscope (POM). The results demonstrated that the crystallinity and crystallization rate decreased with the increase of molecular weight, while the equilibrium melting point increased with the increase of molecular weight. It reached equilibrium when the molecular weight was higher than 55427g/mol. Rheological tests showed that the increase of molecular weight improved the elasticity and decreased the viscosity of the material. The mechanical properties test showed that the secondary yield phenomenon occurred in all samples under uniaxial tension. The yield strength increased with the increase of molecular weight, while the elongation at break increased first and then decreased. This work is important for the acquisition of excellent performance biological PTT polyester with practical value.