Abstract: The antenna array of the large phased array radar is characterized by large aperture, heavy weight and high accuracy, which puts forward higher requirement for the machining accuracy and outfield construction. Both the manufacturing process and outfield installation have the problems of high cost, long period and difficult to achieve. In this paper, a new installing & adjusting method is proposed for the antenna array of the large phased array radar. In the method, a small-volume and light-weight installation block is used to replace the large skeleton. The optical instrument is adopted here to guide the installation instead of machining location. And the adjusting mechanism is used to replace the adjusting spacer. As a result, the cost is lower, the installation accuracy is improved, the construction difficulty is reduced and the development period is shortened.