An integrated mathematical simulator for hot strip mills has been developed. This Hot integrated Mathematical Simulator (HIMS) can estimate simultaneously temperatures of rolled material and roll, rolling loads such as rolling force and torque, and metallurgical properties of rolled material from the exit of reheating furnace to the coiler. The HIMS consists of three simulators of Temperature, Rolling and Metallurgy, and it takes coupling relations between the above three simulators into consideration to obtain accurate results. (1) The Temperature Simulator is used for calculating the temperature changes of rolled material and roll. (2) The Rolling Simulator is used for calculating the force, the torque, the motor power, the deformation resistance, the strain distribution in the thickness direction, etc. during rolling. (3) The Metallurgy Simulator is used for calculating changes of austenite (γ) grain size and phase transformation, and mechanical properties such as yield strength (Y.S.), tensile strength (T.S.), elongation (El.) and Vickers hardness (Hv) at room temperature. At present, the HIMS is used as an effective tool for solving various problems of hot strip mills, because its application field is very wide.