In order to study the earthquake cycle, it is necessary to approach the grain size characteristics of lake sediments. The sediments in the Diexi ancient lake located at the upstream of the Minjiang River contain a lot of information about climate and geological environments. The soils in the disturbed layers and the underlying layer (lower contact layer) with obvious disturbance characteristics in the full section cores of the Diexi ancient lake are analyzed by using the methods such as ground investigation, core observation, measurement and dating of particle size and climate analysis. The results show that there are ten obvious disturbed layers, whose disturbing phenomena are the same with that outcropped on the surface of the Diexi ancient lake. The particle size in the disturbed layer is larger than that in the lower contact layer. The particle diameter (d_(50)) of the sediments in the disturbed layers is 0.0068~0.0107 mm and that of the most sediments is about 0.008 mm. The silt content of the disturbed layers fluctuates a lot and the mass fraction of its underlying layer powder is mostly about 64%. On the other hand, the mass fraction of the clay in the disturbance layers is about 33%, while that of the underlying layer fluctuates a lot. The characteristics of these disturbance layers and underlying layers reflect the changes of the lacustrine sediments under the influence of the external force during the deposition process. Combined with the data of the age dating, the result of the initial speculation about the earthquake cycle is about 850 a.