The invention relates to a method for producing ultrathin low-carbon steel by use of a thin slab casting and rolling process. The method comprises the following steps: continuously casting molten steel into a continuous cast billet with the width of 1,300-1,600 mm and the thickness of 60-100 mm; then sequentially conducting rough rolling, heat preservation by a heat holding cover, induction heating, high-pressure water phosphorus removal and finish rolling to obtain ultrathin strip steel with the width of 1,300-1,600 mm and the thickness of 0.8-1 mm; and finally, performing controlled cooling, roll-dividing cutting and roll take-up. A produced ultrathin low-carbon steel end product has the yield strength of 250-310 MPa, the tensile strength of 350-400 MPa and the ductility of larger than or equal to 35%. By adoption of the method, stable production of hot-rolled ultrathin low-carbon steel with the thickness of 0.8-1 mm can be realized, the dimensional accuracy, the flatness accuracy and the comprehensive mechanical property can be improved, the demand for 'replacement of cold product by hot product' is met and the production cost is lowered.