An integrated process modelling system for simulating the microstructure evolution of Nb-microalloyed HSLA steel produced in CSP hot rolling process has been developed on the basis of the microstructure simulation and mechanical properties prediction technology.3-D thermomechanical coupled finite element models for simulating hot strip rolling have been developed and the distribution of equivalent plastic strain through the thickness direction of the rolled material by CSP rolling was obtained.Thus the distribution of temperature,strain and strain rate through the thickness of the steel stocks,as well as the microstructure evolution during hot rolling of X60 line pipe steel strip has been investigated by using the developed integrated process modelling system.In addition,the determination and optimization of controllable process parameters during CSP hot strip rolling for the Nb-microalloyed X60 line pipe steel have been implemented,and control strategies such as adopting larger pass reduction in the first stand,arranging appropriate pass interval times and proper rolling speed,to reduce or eliminate mixed grain microstructure of Nb microalloyed strip in CSP processing have been proposed. An integrated process modeling system for simulating the microstructure evolution of Nb-microalloyed HSLA steel produced in CSP hot rolling process has been on the basis of the microstructure simulation and mechanical properties prediction technology. 3-D thermomechanical coupled finite element models for simulating hot strip rolling have been developed and the distribution of equivalent plastic strain through the thickness direction of the rolled material by CSP rolling was obtained. Thus the distribution of temperature, strain and strain rate through the thickness of the steel stocks, as well as the microstructure evolution during hot rolling of X60 line pipe steel strip has been investigated by using the developed integrated process modeling system. In addition, the determination and optimization of controllable process parameters during CSP hot strip rolling for the Nb-microalloyed X60 line pipe steel have been implemented, and control strategies such as adopted larger pass r eduction in the first stand, arranging appropriate pass interval times and proper rolling speed, to reduce or eliminate mixed grain microstructure of Nb microalloyed strip in CSP processing have been proposed.