Abstract: Composite materials are widely used in the aerospace field; however, their relatively low resistance to impact makes impact localization and monitoring of composite structures critically important for ensuring aircraft operational safety and controlling maintenance costs. To address the limitations of conventional time-reversal focusing imaging methods—namely, the large number of sensors required for large-area impact localization, which leads to excessive additional weight of the sensing network and high computational burden—a lightweight two-stage imaging localization method for impact on composite structures was proposed. In the proposed approach, the time-of-flight difference features of two narrowband impact signals at different frequencies are extracted using the Shannon wavelet transform to perform first-stage imaging for impact radius estimation. Locations with high pixel values in the first-stage imaging results are regarded as potential impact regions. Based on these regions, time-reversal focusing–based second-stage imaging is subsequently conducted to achieve accurate impact localization, while significantly reducing the imaging computational cost. Experimental validation was carried out on a 900 mm × 900 mm composite plate instrumented with five piezoelectric sensors arranged as a sparse array. The results indicate that, for 20 impact locations, the proposed method achieves an average localization error of only 1.4 cm, and the average imaging computation time is reduced by 96.2% compared with the conventional time-reversal focusing imaging method. The proposed method enables accurate impact localization in large-area composite structures with substantially reduced computational cost.