Using the wind observation data of automatic weather stations (AWSs) in Zhejiang Province during December and February from 2010 to 2014 and the retrieved ASCAT winds, and by means of the Fuzzy Cluster Mean (FCM), an offshore wind speed calculation formula is established and the error analysis for ASCAT products during cold air events in the Zhejiang coast is carried out. The results show that the most AWSs in northern Zhejiang coast have a southerly vector difference compared with the winds at Zhoushan Buoy, the AWSs in the southern coast have a southeasterly vector difference compared with the Wenzhou Buoy, and the AWSs wind speeds generally are smaller than wind speeds from the buoys. The analysis also indicates that altitudes impact little the wind speed differences (δ) between the AWSs and buoys, and the distance of the stations from the coastline is the main factor that impacts the δ value. When cold air strikes the Zhejiang offshore, the distribution of the correlation coefficients between the ASCAT and observations has the characteristics of paralleling to the coastline and increasing from the west to the east. Generally, the distance from the stations to the coastline is usually more than 30 km when coefficients are more than 0.5. The observed winds from Zhoushan and Wenzhou Buoys have a good correlation with the retrieved ASCAT winds. But there is a large special difference in the ASCAT winds error in Zhejiang offshore. The distribution of the corrected ASCAT wind speed also has a characteristic of paralleling to the coastline and increasing from the west to the east, and its absolute error is less than 2 m·s-1 compared with the observed speed.