Abstract: Discusses the effects of TMCP parameters, i.e. the processing parameters, on the microstructure and mechanical properties of high-strength structural steel. And the strengthening/toughening mechanism of the steel is investigated by virtue of optical microscope, SEM (scanning electron microscope) and EBSD (electron backscattered diffraction). By choosing properly the parameters of the two-stage controlled rolling and accelerated cooling process, the high strength structural steels were obtained coming up to China's National Standards Q690, Q620 and Q550 as included in GB/T16270-1996. The regression equations describing relationship between such processing parameters as finish rolling/cooling temperature, cooling rate and mechanical properties are thus given, and how those parameters affect the microstructure and mechanical properties are analyzed. The results showed that the steel plates can be up to the standard Q550 if the finish rolling temperature θFR=870-880°C, cooling rate vC=15-20°C/s and finish cooling temperature θFC=570-600°C; up to Q620 if θFC=500-570°C with other conditions unchanged; up to Q690 if vC=35-40°C/s and θFC&asyum;550°C with θFR unchanged.