A optical approach to generate microwave signals with multiple modula tion formats using a Mach-Zehnder modulator (MZM) is proposed and demonstrated.In the prop osed approach,a microwave signal and an encoded rectangular wave signal are simultan eously sent to an MZM via a coupler.By properly setting the amplitude of the encoded signals, the MZM can operate at different transmission points in its transmission curve,which leads to the generation of microwave signals with multiple modulation formats,such as frequency-shift key ing (FSK),binary phase-shift keying (BPSK) and frequency-doubling BPSK.Only a single MZM is required in the proposed scheme,and no frequency-dependent electrical devices o r wavelength-dependent optical devices are applied.Therefore,the scheme has compa ct structure and large frequency tunability.Specifically,frequency-doubling BPS K microwave signal can be generated in this structure as well,which will make our scheme to meet the demand of higher frequency applications.In the experiments and simulations,the FSK micro wave signal at 10/20GHz,BPSK microwave signal at 10GHz and frequency-doubling BPSK microwave signal at 20GHz are respectively generated,which verifies the feasibility of the propose d approach.