The invention discloses a flame cutting technology for thick steel plates. The flame cutting technology comprises the steps of 1, determining the height of a cutting rack before cutting and grinding and polishing rails; 2, setting the cutting speed according to the string formula that V is equal to kD plus d, wherein k is -1.5, d is 350 and the cutting thickness ranges from 10 mm to 120 mm; 3, adopting the mixed gas of oxygen gas and propane, controlling the length of flames to be 10+/-2 cm and guaranteeing that the proportion of red flames (the head parts) to blue flames (the root parts) of the flames is 1 to 9; 4, carrying out measuring, length-fixed cutting and marking-off on the steel plates, adjusting the positions of cutters to align to the marking-off position and guaranteeing the width of the two cutters of a cutting machine through supporting arms; and 5, after cutting is completed, rechecking the sizes of the steel plates, wherein the width expansion range is 4-8 mm, and the length expansion range is 10-25mm. According to the flame cutting technology, the problem of cutting explosion generated in the cutting process of the thick steel plates can be reduced, the cutting accuracy can be controlled, the cutting quality can be improved, and the product size and the product quality can meet the standard requirements.