Abstract: The Microwave Imager Combined Active and Passive (MICAP), the first ocean salinity detection satellite in China, realizes the global scale measurement of key geophysical elements such as ocean salinity and soil moisture through multi-factor fusion inversion. The high-sensitivity L-band one-dimensional Synthetic Aperture Radiometer (SAR), serving as the primary detector for MICAP, features a digitally implemented subsystem with a distributed architecture that constitutes the core module of the radiometer’s receiving chain. The subsystem’s key performance indicators directly affect the measurement accuracy of both the radiometer and MICAP in detecting ocean salinity, thus the mission imposes stringent performance requirements. This study addresses the high-precision performance testing needs of the distributed digital subsystem, focusing on challenges such as synchronized multi-node data acquisition under a distributed framework and separation of hardware-software coupling performance. The testing method employs multi-device synchronous triggering and the Integrated Logic Analyzer (ILA) tool embedded in the FPGA of front-end data acquisition units to achieve synchronous capture of original AD sampling data from 24 channels across multiple individual units. This solution resolves the absence of original data aggregation points among multiple front-end data acquisition units in the distributed architecture. Furthermore, the study proposes a bidirectional verification framework for both hardware and system-level performance. The hardware performance is tested by analyzing raw acquired data, while the integrated hardware-software performance is evaluated by processing the end-to-end scientific data packets. This methodology achieves decoupled testing of the hardware and software performance of the distributed digital subsystem. The actual test results, including amplitude consistency ≤0.4 dB, phase consistency ≤1º, and correlation bias ≤–38 dB, meet the mission's specified requirements. The research results have been applied to the MICAP engineering development, providing critical technical support for the performance verification and optimization of the distributed digital subsystem of ocean salinity satellite synthetic aperture radiometer.