Abstract Many ultra high voltage (UHV) AC power transmission projects have been put into commercial operation successfully in China. By the end of 2019, a backbone of UHV AC power grid has been built in the vast area of Sanhua (North, Central and East China). China proposed the target of developing UHV transmission technology at the end of 2004. The first UHV AC transmission project was put into service in January 2009 named as Jindongnan-Nanyang-Jingmen UHV AC demonstration project. At present, a lot of UHV AC transmission projects have been finished step by step in China which has experienced three stages of technological breakthrough, scale construction and improvement. Relying on engineering practice, China has mastered a full set of core technologies for UHV AC transmission from planning and design, equipment manufacturing, construction, installation, commissioning and testing to operation and maintenance, and a complete set of UHV AC equipment representing the highest level of international electrical equipment manufacturing has been successfully developed, and established the high voltage and strong current test capability with the most complete function and the highest test parameters as well as the standard system of UHV AC transmission technology. In this paper, China's UHV AC transmission technology and its engineering application achievements were presented including the UHV AC engineering design, equipment development, construction and standard system construction etc.