This intensity distribution of rainbow at different temperature and its application in grain size measure are investigated theoretically and experimentally. The results show that scattering intensity distribution of droplet is not simply second-order rainbow distribution while refractive index is around 1.33 with scattering angle between 117° and 134°, but the interference distribution between second-order and fifth-order rainbow. According to the spectral characteristics of scattering intensity, the method of reconstructing intensity of the second order and fifth order rainbows from interference intensity spectrum is presented