Abstract: Traditional array antenna fault diagnosis methods require measurement data with both amplitude and phase information, while phase measurement is usually expensive and technically infeasible. To address this issue, an array antenna fault diagnosis method with phaseless measurements is proposed in the paper. The proposed method first constructs a phase error matrix and introduces it into the forward model of the array antenna, thereby, obtaining a signal model with unknown phase information; based on this signal model, the phase error matrix and array element excitations are iteratively solved, ultimately achieving the goal of diagnosing faulty elements of the array antenna. Numerical simulations demonstrate that the proposed method is superior to traditional array antenna fault diagnosis methods in terms of accuracy, effectiveness and robustness. The proposed method has important application prospects.