Abstract: SPI(Serial Peripheral Interface) technique is u sed for communication with various peripheral devices. This kind of communicatio n mode employs three-wire connection and full duplex synchronous data transmiss ion. It has the features of less link, fast speed, high reliability and etc. The beam steering system of the phased array radar not only controls the phase shif t of the modules on the array of radar but also monitors their operation state. SPI technique is widely used in the beam steering, and can realize monitoring on the whole array be the beam steering system through high-speed, real-time, re liable data exchange between sub array and modules, and monitoring on the module s at the sub array level.