A deceptive jamming method based on convolution technique is proposed in order to implement effective image deception jamming for low frequency ultra wideband Synthetic Aperture Radar(SAR). Based on the SAR target echo characteristic, analytic formula of the modulation function is derived. The approximate processing is required when the jamming signal generated. For a low frequency ultra wideband SAR, the echo signal is strongly coupled because of the wide beam. Considering the usual imaging algorithm used in ultra wideband SAR, the jamming modulation function is accurate to the cubic phase. And the coefficients of each term are analyzed and simplified. Finally, two simulation examples are given to show the necessity of improvement and the effectiveness of the jamming technology. Both the theoretical analysis and simulation results show that the improved method can effectively implement the false image jamming for ultra wide band SAR.