Abstract: The low-frequency phased ultrasonic detection technology used for quantitative analysis of detects in ship composite material is studied. First, the phased array focused sound field of typical ship composites is studied, including the influence of sound speed on small defect detection ability, the influence of frequency and synthetic aperture on near-field length, and the simulation analysis of sound field with different focus depths. Second, the recommendation principle of ultrasonic frequency and synthetic aperture for typical ship composites with different thickness are proposed. To verify the accuracy of the principle, the Φ3 mm defects are actually detected, and the TCG curve is used to verify the detection effect. The quantitative analysis for the near-surface and internal defects of the typical ship materials is realized, and the recommendation principle turns out to be effective.