Based on cascade Mach-Zehnder modulators(MZMs), a broadband microwave frequency down-conversion method was proposed, and the target distance information was derived from the down-converted intermediate frequency(IF). In the proposed scheme, a linear frequency modulated microwave signal was multiplicated by controlling the bias point and modulation index of MZM. The multiplicated sig. nal was then transferred through an electric time delay to simulate the retuning signal of the target, and the transferring delayed optical sidebands are modulated on MZM. The IF signal carrying the target distance information was obtained after a low-pass filter. Analogous simulations of frequency doubling, quadrupli. cating, and sextupling of central frequencies of 10. 8, 21. 8, and 32. 4 GHz and bandwidths of 2. 7, 5. 6, and 8. 4 GHz are achieved. Moreover, as the electrical time delay increases, the IF linearly decreases. The proposed method is proven to be flexible, highly accurate, and easily implemented, demonstrating its great potential in radar systems for wideband imaging systems.