The sudden shortterm severe precipitation, frequently caused by mesoscale and microscale weather systems, is very complicated to forecast quantitatively. This study develops a seamless quantitative precipitation forecasting (QPF) model based on the rapid rolling update technique. In the developed model, the quantitative precipitation nowcasting (02h) is based on the improved optical flow method, the shortterm quantitative precipitation forecasting (212h) is based on the GRAPES3km and realtime frequency matching correction method, and the short and medium range quantitative precipitation forecasting (12240h) is based on the generation technique of optimal background precipitation field. According to forecasting skills of three methods in different forecasting time, the forecast fusion technology based on the empirical weight function is developed for the seamless quantitative precipitation forecasting (0240h) with the realtime precipitation verification and QPF. The 24hour quantitative precipitation forecast from May 2018 to October 2018 is taken as the experimental case to test the developed model, and the result is compared with forecasts of the traditional model. Results show that the 24hour precipitation forecast accuracy of the developed model is higher than that of the traditional forecast model, especially for the shortterm quantitative sudden severe precipitation forecasting caused by mesoscale and microscale weather systems. It is conducive to the flood forecasting, disaster prevention and control of small to mediumsized rivers.