The invention relates to a laminar flow cooling system for hot rolling, in particular to a laminar flow cooling upper-spraying shielding device. The laminar flow cooling upper-spraying shielding device for reducing pressure surge comprises a plunger piston and a cross beam. The top of the cross beam is provided with a plurality of pressure releasing holes, wherein the pressure releasing holes communicate with plunger piston holes. The plunger piston comprises a connecting assembly section, a back shielding section, a pressure unloading section and a front shielding section, wherein the connecting assembly section, the back shielding section, the pressure unloading section and the front shielding section are connected in sequence in the axial direction. The outer diameters of the back shielding section and the front shielding section are matched with the inner diameters of the plunger piston holes. The outer diameter of the pressure unloading section is less than the inner diameters of the plunger piston holes. By means of the laminar flow cooling upper-spraying shielding device for reducing the pressure surge, laminar flow cooling water is shielded, cooling width is adjusted, meanwhile, by using the principle of flow separating and pressure releasing, under the premise that the cooling width adjusting is not influenced, the laminar flow cooling water in a collecting pipe is discharged from the pressure releasing holes through the small diameter part of the plunger piston, so that the pressure surge of the laminar flow cooling water is reduced, control of cooling parameters is more precise, control errors are reduced, and the uniformity of strip shape, mechanical performance, temperature and phase change of strip steel in the width direction is ensured.