The invention relates to a preparation method for a curved-surface composite material preform. The preparation method comprises the following steps: a, manufacturing a mould; b, measuring length L1 of a longest bus in the length direction of the mould and length L2 of the longest bus in the width direction of the mould; c, manufacturing planar three-dimensional fabric; d, laying the planar three-dimensional fabric on the mould; e, drawing thread ends at the two sides of weft yarns in sequence, and straightening the bus, in the width direction of the mould, of the weft yarns; f, drawing thread ends at the two ends of warp in sequence, and straightening the bus, in the length direction of the mould, of the warp; and g, if the yarn is bent, repeating the steps e and f until the yarn is completely straightened relative to the bus. The preparation method has the beneficial effects that a phenomenon of forming penetrating holes in the thickness direction of the fabric due to yarn adding and reducing of a conventional curved-surface composite material perform can be effectively solved, and the inner quality of the product is guaranteed; and the density uniformity of the fabric is improved, the forming process is simplified, and quick forming can be realized.