Abstract: Addressing the need for low-cost attitude measurement with unmanned surface vehicle (USV) mobile measurement systems under weak global navigation satellite system (GNSS) signal conditions at sea, this study simulates a weak GNSS signal environment and conducts dynamic experiments with multi-antenna GNSS on USVs. The feasibility of multi-antenna GNSS attitude determination in weak signal environments at sea is verified through data analysis. An improved least squares method for multi-antenna network adjustment is applied to process the multiple antenna GNSS attitude data, and the accuracy is evaluated. The experimental and analytical results show that the method of attitude calculation by switching baselines in weak signal environments is feasible, with discrepancies in the computed attitude results not exceeding 0.01°. Moreover, the accuracy of attitude angle calculation in three axes can reach 0.1973°, 0.0421°, and 0.0694° using the least squares method of four antenna network adjustment.