Abstract: The electrical tree is a typical defect of XLPE HVDC cables. Effective detection of the tree is of vital importance for the evaluation of cable insulation status. In this paper, DC partial discharge (PD) experiments were carried out on the XLPE insulation samples with electrical trees. The characteristics of PD at different stages and voltage parameters were analyzed. It is found that PD occurs in the samples with electrical tree defects during the DC voltage drop, while the samples without electrical trees have no PD. The polarity of the PD during the voltage drop is opposite to that in the constant voltage stage. The PD shows good repeatability and has a negligible effect on the tree size. The experiment shows that the PD detection in the voltage drop stage can provide a reference for the evaluation of the electrical tree of HVDC cables. In addition, the experiment shows that multiple PD may lead to the increase of tree conductivity and PD extinction voltage. The experimental results of different voltage parameters show that higher DC voltage and appropriate voltage reduction rate can increase the PD number. The average PD amplitude is higher when the needle electrode suffers negative voltage. Constant voltage duration time has a negligible effect on PD characteristics. Numerical simulation was used to analyze the electric field in the insulation during the voltage drop. The study shows that the attenuation rate of the Poisson electric field is lower than that of the applied electric field in the early stage, which results in the formation of a reverse electric field with high intensity around the needle tip, thus resulting in PD during the voltage drop.