The invention belongs to the technical field of smoke denitration (namely NOx removal), and relates to a modular selective catalytic reduction (SCR) denitration rectification grating device, which is characterized in that longitudinal gratings and transverse gratings of rectification modules are in crossed connection mutually to be fixed and have a grid-shaped structure in which a plurality of hollow thin-wall pipes are arranged and connected regularly and mutually, and the axial directions of the hollow thin-wall pipes are consistent with the height directions of the rectification modules; asealing element is divided into an internal sealing element and an external sealing element; the internal sealing element is positioned in gaps among the rectification modules; and the external sealing element is positioned between the rectification modules and the inner wall of an SCR reactor. The invention has the advantages that after smoke passes through the modular SCR denitration rectification grating device, the flow direction and flow speed distribution of the smoke mingled with dust achieve an ideal effect; meanwhile, the dust in the smoke cannot be accumulated on the rectification grating device; and the rectification grating device is easy to manufacture and low in comprehensive investment cost, and is not needed to be overhauled or maintained, the cost of materials is low, andthe flow field performance of the smoke is improved, so the NOx removal performance of the system is improved.