By using the surface observational data, typhoon track data and ECMWF global reanalysis data, as well as the objective synoptic analysis technique (OSAT), tropical cyclone (TC) track similarity area index (TSAI) and the airflow trajectory model (HYSPLIT4.9), this paper analyzes the characteristics and the causes of the extreme precipitation created by the Severe Typhoon Fitow over the coastal region of Southeast China, and reveals the intensification role of binary typhoons in extreme precipitation. First, Fitow causes the maximum daily precipitation of 395.6 mm in Yuyao and Fenghua, which ranks the second daily extreme TC precipitation in Zhejiang Province in record. Two distinct intense precipitation stages are found in the precipitation process. Secondly, such intense and continuous rainfall during and after Fitow’s landfall is mainly due to the existence of Super Typhoon Danas. In the first stage of the severe precipitation the interaction of the binary tropical cyclones contributes to the extremity, causing Fitow to move much faster than before. Moreover, Danas transports about 79% moisture to the raining region, acting as an important contributor to the extreme precipitation over the southern coast of Hangzhou Bay. In the second stage, as the circulation of Typhoon Fitow almost dissipates, the combined interaction of Super Typhoon Danas and cold air causes the occurrence of the extreme precipitation.