This paper proposes a modified stripmap synthetic aperture radar (SAR) signal processing algorithm with an X-band SAR system, using the practical measurement results of automobile-based SAR (Auto-SAR). The quality of the image is degraded due to an unexpected direction change or anisotropy of the target position in radar image measurement. To solve the quality problem, signal processing is required for the vector velocity of each range in the azimuth direction. An X-band chirp pulse system was implemented and optimized by a signal processing algorithm suitable for high resolution. The stripmap SAR images are produced in five places. The validity of the proposed algorithm is verified by comparing impulse response function analysis and experimental images.