A control method for a middle thickness plate laminar cooling chain edge masking device is disclosed, belonging to the field of rolling automatic control technology and comprising the following steps of: (1) determining a basic value MB of the amount of middle thickness plate laminar cooling chain edge masking; (2) correcting the masking amount with MB' being equal to MB.f(3); calculating the masking amount Mi of each group of opening manifolds; (4) implementing the masking amount of the single manifold; and considering that a masking baffle plate moves to a set masking location when a moving pulse Iact of the i group of manifold is equal to a target setting pulse Ind of the i group of manifold, in order to realize accurate positioning for the masking device of single group of manifold. The invention can achieve accurate control for the location of the edge masking baffle plate of the single group of manifold; a masking policy model takes parameters like thickness of steel plate, width of steel plate and cooling water amount into consideration, and has high model setting accuracy; the method can compensate and correct the system effectively and improve uniformity of controlling width temperature of the steel plate. The invention is suitable for hot-rolling middle thickness plate and laminar cooling device after rolling.