The invention provides a UHVDC (Ultra High Voltage Direct Current) line ground three-dimensional composite electric field calculation method capable of considering terrain influence. The method comprises the following steps: S1: firstly, simplifying a complex terrain into an undulant three-dimensional ground, and establishing a three-dimensional composite electric field calculation model; S2: selecting any one calculation point on the ground, and utilizing a three-dimensional nominal electric field obtained by a moment method to determine an electric line of force from the point back to the surface of a lead; S3: setting an electric charge density initial value of the surface of a transmission lead, and obtaining the electric charge density and the nominal function of each point from the surface of the transmission lead along the space of the electric line of force; S4: updating the electric charge density of the surface of the lead until an average value of the spatial electric charge density meets a limitation condition; and S5: according to the obtained electric charge density and the nominal function, calculating a three-dimensional composite electric field on a complex ground. The method is based on a Deutecsh hypothesis principle and is combined with the moment method, influence on the three-dimensional composite electric field by the complex terrain is considered in a calculation process, and electromagnetic environment evaluation carried out when a UHVDC transmission line goes through the complex terrain can be realized.