Abstract: Grain scattering noise in polycrystalline materials is a key factor affecting the quality of ultrasonic array imaging. Voronoi-diagram-based finite element models suffer from low computational efficiency in array inspections because each array element must be explicitly defined. To address this issue, this paper derives a scattering echo frequency response model that incorporates grain size and grain number. Based on this model, a linear ultrasonic array detection model for scattering noise is established by integrating array delay focusing with the full matrix acquisition (FMA) mechanism. Compared with the Voronoi diagram model, the proposed model cannot simulate variations in grain orientation; however, it offers a clear advantage in computational efficiency and is better suited for system-level analysis of array imaging. Using the proposed model, the effects of grain size and excitation frequency on defect imaging quality are analyzed. An increase in either grain size or detection frequency enhances scattering noise and degrades imaging quality. The experimental results are consistent with the model predictions.