The invention discloses a method and a system for determining a conductor type of a 750kV four-circuit transmission line of the same tower. The method includes: setting up the calculation model of audible noise and radio interference of 750kV four-circuit transmission line without considering the influence of elevation, calculating audible noise and radio interference levels, selecting a variety of alternative phase sequence layout schemes, by combining the electric field strength, determining an optimal phase sequence arrangement scheme, and then obtaining the optimized conductor types satisfying the requirements of electromagnetic environment control at different altitudes through altitude correction, determining the optimal conductor type by economic verification of the transmission line corresponding to the optimal conductor type, which avoids the shortcoming of considering electromagnetic environment only, and provides important technical support for ensuring the environmental friendliness of the project and improving the project economy. The invention is not only suitable for determining the transmission line in the northwest of China, but also can be used for determining ultra-long-distance transmission line conductors such as global energy internet, and has good applicability and high application and popularization value.