Based on a thermal segregation treatment, a novel semiquantitative method for the characterization of the crystalline segment distribution in branched polyethylene copolymers was established by the results of differential scanning calorimetry being treated with the Gibbs-Thomson equation. The method was used to describe the segment distribution of Ziegler-Natta-catalyzed linear low-density polyethylene (Z-N LLDPE), metallocene-catalyzed linear low-density polyethylene (m-LLDPE), and a commercial linear low-density polyethylene with a wide molecular weight distribution. The isothermal crystallization kinetics of Z-N LLDPE and m-LLDPE were studied to assess the effect of different segment distributions. According to their molecular characteristics, the crystallization behaviors were analyzed. They indicated that the different segment distributions of the two polymers resulted in different crystallization processes, including the nucleation and growth of crystals under various crystallization conditions.