Although the pressure differential sensor could estimate the amount of DPF soot load, the accuracy of soot estimation deteriorated seriously at the lower exhaust volumetric flow because of its nonlinear and unsteady state. In order to improve the accuracy, a new soot load estimation method was established to calculate the soot accumulation of DPF for improving the accuracy of the trigger time of active regeneration. This model was based on the balance of engine soot emission and DPF soot oxidation, and which consists of three submodels such as soot emission model, NO₂ passive regeneration model and soot hightemperature oxidation model. Testing validations were conducted based on the world harmonized transient cycle(WHTC). The experimental results showed that the average error between calculated and measured soot load was about 4.6% during the soot load process. The passive regeneration accelerated and active regeneration interval prolonged along with increasing of the exhaust temperature and NO₂ concentration.