Abstract: In the flatness control system of hot strip, measured flatness signals usually contains additional signals caused by temperature difference along the lateral direction of the hot strip after rolling. The lateral temperature of the hot strip was measured by a kind of thermovision in ASP 1700 hot strip mill in AnSteel, China. By analyzing the influence of the temperature difference on the flatness control system of hot strip, the lateral temperature field distributing law was obtained based on the least square method and a temperature compensating model for the control target of strip flatness was set up at the same time.