In recent years, the thermal fractionation techniques play an important role in evaluating chain heterogeneities in semi-crystalline thermoplastic polymers. The temperature rising elution fractionation (TREF) method realized physical separation of different lamellar thickness. To overcome the disadvantage that TREF takes long duration to fractionate polymer chains, differential scanning calorimetry (DSC) is developed to study the degree and distribution of short chain branches on polyolefins. Step crystallization from the melt (SC) and successive self-nucleation and annealing (SSA) are the two most commonly applied methods using DSC. But there are still some problems in the test duration, determination of baseline and accuracy of the result. In this research, we developed a new thermal fractionation method named Step Heating (SH), which needed short test duration and could obtain higher measuring accuracy. We divided the DSC heating program into several heating and temperature holding stages. Because the heat absorption during each heating stage is consisted of heat capacity and crystal melting and the heat capacity changes little during heating, we subtract the heat capacity part from the total heat absorption to get the exact heat absorption due to crystal melting. At low temperature, the polymer lamellar crystals do not melt, so the heat absorption during heating equals to the capacity part. With this method, we could get the fraction of melted crystals during each temperature range within about 1 hour. Furthermore, the step heating method could also manifest the recrystallization behavior of some polymers during the temperature holding stage after the heating stage. The step heating DSC method can be combined with step crystallization or successive self-nucleation and annealing method to give the fraction of melted crystals at each temperature range without the complicated peak fitting procedure.