This study proposes a radar reflectivity factor model considering the effect of turbulent clustering of cloud droplets. A three-dimensional direct numerical simulation of particle-laden isotropic turbulence is conducted to obtain turbulent clustering data. The power spectrum of droplet number density fluctuation, on which the radar reflectivity factor depends, is calculated from the turbulent clustering data. The power spectrum shows strong dependency on the Stokes number. It is confirmed that the proposed model can predict the Stokes number and the wavenumber dependencies of the turbulent clustering effect.