The invention relates to a method for preparing low-carbon stainless steel, which sequentially comprises the following steps of 1, pretreatment of molten iron; 2, K-OBM-S converter smelting; 3, primary LF ladle refining; and 4, molten steel circulating vacuum decarburization: a, a common steel hot tank is used in an RH workbench, b, a bottom argon tube blowing tube begins to vacuumize, c, the vacuum pressure is lowered and oxygen blowing is carried out for decarburization, and the decarburization value is 0.025-0.035%, d, when oxygen blowing is over, the vacuum value is lowered to 40mbar, e, the carbon content reaches the target value of 0.025-0.035%, and restoring operation is carried out at the RH workbench, and f, after fine tuning, wherein the molten steel comprises the following components by mass percent: 0.020-0.030 of C, 0.52-0.58 of Si, 2.40-2.80 of Mn, P less than or equal to 0.030, less than or equal to 0.015 of S, 16.00-16.40 of Cr, 6.00-6.20 of Ni, 2.05-2.25 of Cu, and the balance of Fe and inevitable impurities, and then the molten steel is output, and the temperature of the molten steel is 1540-1550 DEG C. The method for preparing low-carbon stainless steel has high decarburization efficiency, and the content of carbon in the finished product can be 0.03% after decarburization.