High-resolution low-frequency spaceborne synthetic aperture radar is a significant development of SAR technology. Integration time of synthetic aperture and the space varying of echo signal become the key factors that seriously affect the quality of SAR imaging. Traditional signal models and imaging algorithms cannot meet the accurate requirements of low-frequency SAR exceptional imaging. Based on the modified equivalent squint range model and hybrid digital correlation algorithm, a new two-step low-frequency spaceborne SAR imaging algorithm is proposed. The relativity of the two-dimensional (azimuth and range) point target reference spectrum is removed by the improved algorithm, and the precise imaging result is achieved through the first and the residual range cell migration correction steps. A simulation experiment has been conducted to verify the effectiveness of the algorithm.