Ultrasonic guided wave inspection is widely applied in pipeline health monitoring due to its long propagation distance, high efficiency, and suitability for large-scale monitoring. However, dispersion effects and multimode coupling characteristics during guided wave propagation cause echo signal energy dispersion, reducing detection sensitivity for minute defects. The time reversal method enhances defect echo signals by inverting received signals. This study employs COMSOL simulations to analyze the impact of different truncation window widths on time reversal focusing performance. Results indicate that increasing the truncation window width captures more guided wave mode information, significantly enhancing defect echo energy. The defect reflection coefficient improved from 0.3158 to 0.3653, with energy amplification increasing from 2.141× to 2.478×.The study demonstrates that appropriately selecting the truncation window width enhances focusing performance, providing theoretical support for parameter optimization of the time reversal method in pipeline defect detection.