Abstract: The active sub-array is an important factor affecting the maintainability of the active phased array antenna because of the highly integrated structure and complicated telecommunication functions. This paper presents a highly integrated and modular active sub-array on X-band antenna. The design of guiding device on the sub-array improves the reliability of repeated disassembly and assembly of the sub-array. The layered blind plug design is used to avoid the problem of connector misconnection and misplug in the process of assembly and maintenance of the sub-array. Based on the idea of modular maintenance, the line replaceable unit (LRU) is reasonably defined in the sub-array, which ensures the interchangeability of components in the sub-array and improves the efficiency of on-site maintenance. Taking mean time to repair (MTTR) as the index, the maintainability of the active sub-array is analyzed. The results show that the presented sub-array meets the design requirements of fast maintainability of the X-band phased array antenna.