The invention discloses a device and method for correcting deviation of wide-range PK (Pasco-Kennewick) composite box beam cable-stayed bridge assembling slab staggering, and relates to the technical field of construction of wide-range PK composite box beams. The device comprises a reaction frame, a first jack and a second jack, wherein the vertical surface of the reaction frame takes the shape of an asymmetric T; the reaction frame comprises a transverse steel component and a vertical steel component; the transverse steel component and the vertical are both columns with certain bending resistance rigidity; the first jack and the second jack are arranged on two sides of the transverse steel component; top surfaces of the jacks are both in contact with the bottom surface of the transverse steel component; the contact point of the transverse steel component and the first jack serves as a first fulcrum; the contact point of the transverse steel component and the second jack serves as a second fulcrum; the distances between the first fulcrum and the second fulcrum and the axial central line of the vertical steel component are respectively X1 and X2; X2 is greater than X1. By adopting the device and the method, slab staggering between a hoisted Bn beam section and a newly hoisted Bn+1 beam section is eliminated, and the Bn beam section can be precisely matched and connected with the Bn+1 beam section.