Abstract: We study the multi-band non-thermal radiation of PWN G21.5-0.9 using the spectral evolution model.In this model,two electron components are considered,i.e.,a low energy electron component with a power law spectrum and a high-energy electron component with a relativistic Maxwellian plus a high-energy power law tail.We have found that the model can well explain the multi-band observation flux points of PWN G21.5-0.9;moreover,the results show that the radiation from G21.5-0.9 during the band from radio to X-ray is produced through synchrotron emission from the relativistic electrons,and the gamma-ray photons are produced via inversed Compton scattering.