With the rapid development of the radar technology, digital phased array antennas have been widely used in various kinds of phased array radar. Large scale arrays have contributed to the emergence, development and application of sub-array technology. The application of digital sub-array can ensure the performance of array radar system and minimize the system cost and engineering difficulty. Due to the great difference of the principle between digital phased array antenna and conventional analog phased array antenna, the fundamental changes have taken place in the test method. This paper introduces the working principle of digital sub-array. The method for digital sub-array antenna test and the basic structure of the test system are proposed. Meanwhile, the testing steps of important channel targets are elaborated in detail.