Abstract: To address the issue that traditional uniform rain models fail to accurately predict millimeter-wave propagation attenuation in inhomogeneous rainfall environments, this paper proposes a rain attenuation prediction method for the three-dimensional parabolic equation (3-D Parabolic Equation, 3DPE) based on an improved rain cell model. This method constructs an inhomogeneous rain cell structure using the midpoint displacement interpolation algorithm of fractal geometry to restore the spatial distribution of a realistic rainfall field. Meanwhile, it comprehensively considers key parameters including raindrop size distribution, ambient temperature, and raindrop shape, derives the analytical expression for the equivalent dielectric constant of the rain medium, and further corrects the atmospheric refractive index. Finally, a 3DPE rain attenuation prediction model suitable for inhomogeneous rainfall scenarios is established. Characteristic attenuation calculations are carried out based on this model for four typical inhomogeneous rainfall scenarios: convective rainfall, frontal rainfall, stratiform rainfall, and typhoon rainfall. The results show that the model predictions are in high agreement with the recommendation model of the International Telecommunication Union (ITU-R P.838-3) under both horizontal and vertical polarizations. In particular, within the 10-40 GHz Ku-Ka core band for millimeter-wave communication, the deviation between the two is less than 0.5 dB/km.