Abstract: The branching composition distribution and melting-crystallization properties of very-low-density polyethylene PE-VLD with different chain lengths were investigated by means of 13C-NMR spectroscopy and differential scanning calorimetry. The polymerization characteristics of these PE-VLD samples were analyzed on the basis of mean sequence lengths, relative monomer distribution and monomer reactivity ratios, and their crystallization characteristics including lamellar thickness, relative branching degree and crystallinity degree were investigated by SSA thermal classification method. The results indicated that, in the case of PE-VLD with a density of 0.912 g/cm3 and a melt flow rate of 1.0 g/10 min, the sample synthesized by using a butylethylene comonomer exhibited a lower content of copolymerized segment and a lower branching degree than that using a butylene comonomer. However, it had higher crystallinity degree and thicker crystalline lamellas.