The 6 Sigma ET software based on the Finite Volume Method (FVM) is used to simulate the temperature distribution of the down conductor when lightning strikes the ancient building lightning receptor and is discharged along the down conductor. It mainly includes simulation of temperature values and distribution characteristics for down conductors of different materials and diameters respectively under different types of lightning strikes, and a comparison to the ignition point of timber commonly used in ancient buildings is made. The simulation results show that: (1) the temperature rise of down-conductor is not obvious in most cases under short stroke, while it is obvious under the combined stroke. The temperature rise of down-conductor under the combined stroke easily exceeds the ignition point of ancient building timber; (2) when other conditions are the same, the temperature increase of down-conductors is from high to low when different materials are used in the order of steel, medium, and copper; the smaller the diameter of the down conductor, the more the temperature increases after lightning strikes; (3) the farther away from the down-conductor, the lower the temperature becomes; what's more, the rate of temperature reduction falls down with distance, and the temperature is close to normal atmospheric temperature at 10 mm outside the down-conductor; (4) after the lightning current acts on the down conductor, the temperature rises rapidly but drops slowly (the high temperature above 300 ℃ lasts for more than 100 s), and the high temperature during this period can easily ignite the ancient building timber. This study provides a reference for the reasonable selection of down-conductor material for lightning protection of the ancient building, the diameter and the safe spacing between the down conductor and the wooden interface.