The invention relates to a semi-hard magnetic material which comprises alloy components of FeaNibAlcTidMne, wherein a, b, c, d and e are atomic percentages; and the change ranges are as follows: b is not less than 10 and not more than 20, c is not less than 0 and not more than 1.0, d is not less than 0 and not more than 1.0, e is not less than 0 and not more than 1.0, and a is equal to 100-b-c-d-e. The preparation method comprises the following steps of: carrying out vacuum melting and hot-rolling blooming on the alloy components, then carrying out cold rolling and continuous annealing treatment, wherein the first cold rolling deflection is 60-80 percent; then carrying out second cold rolling, and rolling into a steel belt with the thickness of 0.05-0.06 mm, wherein the cold rolling deflection is 95-99 percent; and carrying out gas-protective continuous heat treatment as final heat treatment to prepare the semi-hard magnetic material product. The detailed preparation method is shown as a specification. The semi-hard magnetic material is mainly used for manufacturing an offset magnetic sheet of an acoustic-magnetic anti-theft tag, and the offset magnetic sheet is used for an anti-theft tag of a magnetic-machine type electronic article anti-theft system and achieves the aims of activating the alarm and deactivating unalarmed tags.