The invention belongs to a cure shrinkage suppression technique for thermosetting resin-based composite material for liquid molding and relates to a method for reducing cure shrinkage rate of a resin matrix for liquid molding. According to the invention, aromatic diamine benzoxazine resin with good chemical reaction characteristics and good molecular structure compatibility to epoxy resin, bismaleimide resin and cyanate ester resin is added into the matrix resin as a cure shrinkage suppression component so that the low-cure shrinkage rate component involves in curing cross-linking reaction of the original resin matrix, the cure shrinkage rate of the matrix resin is greatly reduced by structure regulation of the curing cross-linked molecules of the matrix resin, and simultaneously the heat resistance, mechanical property and molding manufacturability of the original matrix resin are not influenced.