The application situations of diameter-extended conductor for UHVAC transmission line projects were presented. Based on 1 000 kV Ximeng-Nanjing UHVAC transmission line project, the electrical characteristics, mechanical performances and the economic features of diameter-extended conductor and conventional conductors were compared. The results show that the diameter-extended conductor not only meets the electromagnetic environment requirements, but also can effectively reduce the project investment for UHVAC transmission line projects, under the precondition of satisfying the transmission capacity, which has great practical significance for the construction of environmentally friendly and resource-saving UHVAC transmission lines.