The invention relates to a manufacturing method for a steel rotational moulding storage tank with a modified polypropylene inside liner. The method comprises the following steps: welding, tapping, polishing, welding a wire mesh, arranging a rolling ring, adding modified polypropylene powder, heating and autorotating, rocking and autorotating, cooling, offloading, removing the rolling ring, trimming and the like. In the invention, the storage tank obtained by the method exactly overcomes the shortcomings of the prior art, the steel rotational moulding storage tank with the modified polypropylene inside liner has not only the strength of steel but also the corrosion resistance of polypropylene plastic, and the inside liner of the steel rotational moulding storage tank has obvious characteristics of good compactness, high mechanical property, high integrity, no joint, no welding line, uniform thickness, high temperature and low temperature resistance, negative pressure resistance, strong adhesion, corrosion resistance, impact resistance, no toxicity, easy maintenance and the like.