The invention discloses a method for reducing water-soluble zinc in zinc-containing slag produced in zinc hydrometallurgy. The method is characterized in that the method comprises steps that: A, zinc-containing slag in a pulp state is subject to primary press-filtration in a box-type filter press, such that primary filtrate and filter residue are obtained; the filter residue is left in the box-type filter press; B, the primary filtrate obtained in the step A is delivered back to a leaching process; the filter residue left in the box-type filter press is combined with pulped zinc-containing slag additionally pumped into the filter press, and secondary press-filtration is carried out, such that secondary filtrate and filter residue are obtained; C, the secondary filtrate obtained in the step B is combined with the primary filtrate; the mixture is delivered back to the leaching process; one part of the obtained filter residue is delivered to a pulping tank, and prepared pulped zinc-containing slag is delivered to the box-type filter press; the other part of the filter residue is delivered back to a lead system or a zinc system in which valuable metals are recycled, such that a press filtration period is accomplished. In the pulping process, a pulping temperature is controlled at 40 to 70 DEG C, and a liquid-solid ratio is controlled at 2-6:1. The method provided by the invention is mainly used for reducing water-soluble zinc in zinc-containing slag produced in a filtration process of zinc hydrometallurgy enterprises.