<p>The Non-linear Frequency Modulation (NLFM) waveform is known for its ability to reduce side-lobe levels without compromising the signal-to-noise ratio (SNR) or requiring windowing operations in Synthetic Aperture Radar (SAR) imaging missions. However, as SAR technology continues to evolve and operational scenarios grow increasingly complex, there is a rising demand for radar waveforms with improved overall performance. One significant limitation of the NLFM waveform is its restricted Doppler tolerance, which limits its potential application in diverse SAR scenarios. To address this issue, this letter proposes a multi-objective optimization approach based on the NLFM waveform model using Fourier series. The optimization is conducted using the NSGA-II algorithm, grounded in Pareto optimal theory, to fine-tune waveform parameters and resolve conflicts between design criteria. As a result, the optimized NLFM waveform not only maintains low side-lobe levels but also improves Doppler performance, making it more suitable for advanced SAR imaging tasks. Finally, simulation results are presented to demonstrate the effectiveness of the proposed NLFM waveform.</p>