In situ improvement of fouling resistance of the state-of-the-art polyamide reverse osmosis membrane module on the basis of the fouling characteristic of the fluid to be treated is of great practical significance. In this work, in situ modification was performed with the spiral wound polyamide reverse osmosis membrane module for improved fouling resistance to specific foulant. Small molecular monomers of amidosulfonic acid (ASA), diethanolamine (DEA) and piperazine (PIP) were grafted onto the surface of the flat-sheet polyamide-based thin-film composite membrane within the module separately through 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC)-activated amidation of carboxyl groups. The results of fouling experiments indicated that the fouling resistance of the polyamide reverse osmosis membrane module to the model foulants of bovine serum protein (BSA), sodium alginate (SA) and dodecyl trimethyl ammonium bromide (DTAB) could be effectively improved through grafting monomers ASA, IDEA and PIP, respectively, showing significant reduction in declines of membrane flux to aqueous BSA, SA and DTAB solutions by 47.2%, 41.3% and 34.4%. The changes of membrane surface hydrophilicity and negative charge were in charge of the improved antifouling property. The in-situ modification was also found to slightly enhance membrane salt rejection and have nearly no influence on membrane water flux. (C) 2018 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.