The invention discloses a method for calculating the neutral current of a transformer during running of a direct-current power transmission monopole. The method comprises the following steps: establishing a grounding electrode model and a ground soil model, and calculating the surface potential distribution around a grounding electrode; establishing a direct-current circuit model of a power grid; calculating the neutral current of the transformer according to the calculated surface potential distribution and the established direct-current circuit model. According to the method, the grounding electrode model and the ground soil model are established under the consideration of the influence of the coastal effect on the ground soil model in order to calculate the surface potential distribution around the grounding electrode; the direct-current circuit model of the power grid is established, and the neutral current of the transformer is calculated according to a calculated neutral point potential. The method is high in adaptability, can be used for calculating the neutral current of transformers on inlands and coastal regions, can contribute to remarkably increasing the calculating accuracy, and has important practical significance to safe and stable running of the transformer and even an entire system during ground running of the direct-current monopole.