The invention discloses an ultrathin electromagnetic shielding plate and a preparation method thereof. The ultrathin electromagnetic shielding plate comprises at least one magnetic shielding layer, aprotecting film, a double faced adhesive tape layer and a release film layer. The preparation method comprises the steps of fragment preparation and treatment, pavement, embedding and rolling, attachment and rolling and the like. In a preparation process of the disclosed ultrathin electromagnetic shielding plate, complete strips are not required, and the electromagnetic shielding plate can be ultrathin under the condition that electromagnetic shielding is met.