Abstract: In order to determine the history of the F₂₀-fault activity in Ertan, Sichuan province, some samples of calcite veins and nodule were collected within and outside the fault zone, and the age of the calcite was measured by the thermoluminescent technique. Based on the age,occurrence, degree of crystallization and the deformation characteristics, of calcite,the calcite veins in the region could be divided into 3 periodst the first is about 2.25m, y. age, the second 1.0-1.3 m.y.,and the third 0.35 m. y., Then it can be exactly determined that the latest activity of the fault is before the second period calcite intrusion. From then on, no more appa rent activity of the fault has occurred. It has great significance for evaluating seismic risk in Ertan dam region.