The effects of multi-modification on the strength and toughness of 30CrMn2Si cast steel were investigated. The mechanical properties tested include tensile strength; Charpy impact toughness from room temperature to -60 degrees C; hardness and fracture toughness. Microanalyses were carried out by optical microscopy, transmission electron microscopy, scanning electron microscopy, and X-ray diffraction, and included the microstructure and submicrostructure of martensites, residual austenites, the size and distribution of non-metallic inclusions, and the original austenite grain size. It was concluded that, with the hardness unchanged, the fracture toughness of the modified steel was raised to 95 MPa m(1/2), 34% more than that of the un-modified steel, and the impact toughnesses at normal and low temperatures raised to 62 and 61.2 J cm(-2), respectively, 67 and 75% more than those of the un-modified steel. Furthermore, the fracture strength and yield strength of the steel were increased by over 200 MPa.