In order to solve the reliability control problem of thousands of microwave modules in the space-borne Synthetic Aperture Radar(SAR) phased array antenna, a design scheme of beam-steering system based on parallel chain topology is proposed. This solution uses a chain topology bus to simplify unit interconnection and realize lightweight design. It proposes a normalization method of the receiving circuit to realize peer-to-peer interchange of the beam-steering unit, and elaborates the reliability design measures to prevent interface circuit failure from the aspects of DC bias, fault isolation, and synchronous transmission. The test results show that when the threshold value of the receiving chip is 400 mV, the DC bias resistance value should be less than 690 . to avoid the output instability at the receiving end; when any receiving end in the bus fails, a 1 k. isolation resistor can be connected in series to prevent the bus communication from being disabled; when the falling edge of the clock is located at 1/2 of the length of the data symbol, the transmission is error-free. The research results can provide a reference for the reliability design of subsequent space-borne large phased array radar beam-steering systems and other similar space loads.