China is one of the countries in the world with a frequent occurrence of earthquakes. Among all provinces in China, Yunnan province in southwest China has the most frequent occurrence of earthquakes. Located 60 km south of Kunming, the capital city of Yunnan province, Fuxian lake is situated in a region where the Xiaojiang earthquake belt and the Tonghai-Shiping earthquake belt intersect. The Fuxian lake area is the region in Yunnan that has the most frequent occurrence of earthquakes. If we could find a natural recorder of historical earthquakes in the lake deposits of Fuxian lake and explain its mechanism, it means that we have discovered a seismic detector installed by nature in Fuxian lake. It is therefore important for us to discover the evidence in nature. In this paper, proven evidence has been found for the existence of a natural recorder of historical earthquakes in Fuxian lake area—the magnetic susceptibility of lake sediments in Fuxian lake. A 170 cm-long sediment core was taken from Fuxian lake, which was tested to be representing the sedimentation for the past one thousand years from 1 025 to now. In our research, the magnetic susceptibility peaks of the lake sediments correlate to many earthquakes recorded in history that occurred during the past one thousand years. In addition, earthquakes without a record in history have been recovered by testing the magnetic susceptibility of the lake sediments.