The invention relates to a method for casting a thirty-tonnage stainless steel ingot, which comprises the following steps: 1, the casting of the head of the steel ingot: firstly, spreading paper scraps with a thickness of 0.8 to 1.2mm on an entire die seat, then overheating a liquid steel to a temperature of 80 to 100 DEG C, opening a ladle sliding nozzle with the width of 45 to 55mm within 5 seconds, and when the liquid steel rises to the height of 220 to 280mm, increasing the rising speed of the liquid steel to be 105 to 125mm/min; 2, the casting of the body of the steel ingot: before the liquid steel rises to a cap line, not adjusting the ladle sliding nozzle; and 3, the casting of the cap line: after the liquid steel rises to the cap line at the height of 50mm, adjusting the sliding nozzle to the width of 10 to 30mm, opening the sliding nozzle to the width of 40 to 65mm when the liquid steel rises to the height of two thirds of the cap line, then breaking off the steel pouring stream 2 to 5 seconds, and opening the sliding nozzle to the width of 40 to 65mm again, carrying out regenerative cycle operation to perform filling for 3 to 6 times, adjusting the sliding nozzle to the width of 10 to 30mm, and then continuing to carry out filling. The stainless steel ingot casted by using the method of the invention has the advantage of eliminating surface defects such as lapping defect, scab, skull patch and residual shrinkage cavity.