Abstract: The Quanzhou great earthquake of Fujian province in 1604 has been regarded as one of the famous great earthquakes (M=8.0) in China. It is the most important strong earthquake on the seismic belt along south-east coast. According to the study on its historical data and contrast with Nanao earthquake(M=7.3) n 1918, in this paper, we think the magnitude of this earthquake should be etermined to be 7.4.