Abstract: The test terminal is an important part of the electrical performance test of HVDC. Based on the water terminal of AC cable, this paper creates the model of water-oil terminal of DC cable. In order to study the electric field and charge density distribution of the HVDC water-oil terminal under impulse voltage, a simulation model of the electric field-space charge of the water-oil terminal is established. The injection of space charge and the interaction between space charge and electric field are fully considered in this model. Secondly, the correctness of the model is verified by comparing with the experimental data. Finally, the electric field and the charge density distribution under six kinds of impulse voltages recommended by GB/T 31489.1 are studied. Meanwhile, the electric field intensity and charge density at the water-oil interface are compared. It is found that the lightning impulse voltage will generate the largest electric field at the water-oil interface among the six operating voltages, which exceeds the breakdown field intensity of water. Therefore, the water-oil terminal is not recommended to participate in the lightning impulse test. The research provides a valuable reference for design and development of the HVDC test terminal.