A fractal sea model based on non-fully developed full-range sea spectrum (NDFFM), which is believed to be more applicable to the real sea surface, is presented. The two-scale method is used to calculate the backscattering cross-section of the NDFFM sea surface. The distribution of the time-varying scattering amplitude is studied, and the numerical results show that the distribution satisfies K-distribution with higher significant-slope(SS) and satisfies Rayleigh distribution with lower SS. Finally, the results are compared with those of the conventional fractal model and the real radar data, which prove the accuracy and efficiency of this model.