Abstract: A mass trial was carried out for a 780 MPa engineering machinery steel and the microstructures and properties of steel were investigated. The controlled rolling, ultra-fast cooling and laminar cooling process were used based on the optimized compositions of steel, and good microstructures and mechanical properties were obtained. The results showed that ultra fast cooling plus laminar cooling process is used after the finish rolling, and the outlet temperature of ultra fast cooling and coiling temperature are controlled at 650°C and 570°C, respectively. The yield and tensile strengths of steels are higher than 685MPa and 785 MPa, respectively, and good impact resistance, formability and weldability are obtained. The microstructures of steels are composed with ferrite and a litlle of pearlite. A large number of (Nb, Ti) (C, N) precipitates are observed with size less than 10 nm dispersed in the ferrite matrix, and these fine precipitates increase the strength of steel effectively.