Polyacrylonitrile (PAN) precursors have been polymerized at different radical polymerization temperatures for preparing sulfurized-polyacrylonitrile (S-PAN) composite cathodes in rechargeable lithium sulfur battery. The physical properties of these composites have been investigated using X-ray diffraction, Fourier transform infrared spectrometry, Raman spectroscopy, Brunner-Emmet-Teller measurement and Gel permeation chromatography analysis. The electrochemical performance of the S-PAN composite cathodes made from the PAN precursor was investigated. The results showed that the molecular weight distribution of the PAN precursors affected the electrochemical performance of the S-PAN made from the PAN precursor. S-PAN composites derived from PAN with a narrower molecular weight distribution at 65 °C were exhibit the best electrochemical performance in lithium-sulfur battery.