A photonic scheme based on dual- parallel Mach - Zehnder modulator (MZM) and four - wave mixing of a semiconductor optical amplifier (SOA) is propose d to generate microwave signals with a frequency of 24times of that of the radi o frequency signal,with the advantages of wide frequency coverage,simple system structure and high spectral purity . In this scheme,a low - frequency microwave signal modulates the light wave in a dual - parallel MZM in which two sub MZMs and MZM are all biased at the maximum transmission point via adjusting the dc bias to sup press the odd - order sidebands. Then the optical carrier and the second sidebands at the output of the dual -parallel MZM can be suppressed by properly adjusting modulation indices of the MZM and phase shift of the phase shifter, resulting in the generation of the fourth sidebands.The fourth sidebands are then injected into the SOA,the twelf th sidebands would be generated due to the four -wave mixing effect,so that a microwave signal with a frequency of 24times of that of the radio f requency signal can be obtained.Finally,s imulation is performed to verify the feasibility of the scheme.When t he frequency of the driving signal is 10GHz,microwave signal with frequency of 240GHz is achieved.