In order to study the effect of rainfall on 5G millimeter-wave (MMW) communication, a new modified MMW dynamic rain attenuation time series model based on the Weibull distribution rainfall model and the EMB time series model is proposed. The analysis for the subtropical Haikou 78GHz rainfall link performance shows that the simulating time series by newly modified model can effectively characterize the dynamic and statistical properties of MMW rain attenuation. According to this model, an adaptive modulation coding scheme (MCS) is induced which can be applied to rainfall fading links. On the 78G MMW rainfall link, the BER, the spectral efficiency are analyzed. The MCS transform algorithm is presented. Through the simulation analysis, the adaptive MCS for mitigating the effects of rain attenuation is recommended. The scheme can effectively mitigate the effect of rainfall on the MMW link and improve the system spectrum utilization and availability.