This paper aims to enhance the performance of the machine-made flat sheet thin-film composite (TFC) polyamide-urethane seawater reverse osmosis membranes and their spiral wound elements by modifying the manufacture technique. Continuous flat sheet Blouson Belstaff Robert Downey TFC membranes were fabricated employing a reaction line through interfacial polymerization of m-phenylenediamine with 5-chloroformyloxyisophthaloyl chloride on porous polysulphone support membrane under optimum conditions, Belstaff Soldes and spiral wound elements were manufactured from the resulting membrane sheets. In the process, a modified laminating method of one-side-contacting reaction and an additional procedure of thermo-sealing on the membrane sheet along the glue line were adopted for membrane fabrication and element manufacture, respectively. The effects of the modifications involved in the manufacture technique on the performance of the resulting membranes and elements, and the separation characteristics of the machine-made membranes were investigated in terms of permeate flux and salt rejection through permeation experiments with Belstaff Classic Tourist Trophy Beige synthetic seawater. It was found that, the flat sheet TFC membranes and spiral wound elements manufactured adopting the modified technique showed significant improved seawater reverse osmosis performance. Additionally, the results of pilot test on a desalination plant indicated that the developed TFC membranes and spiral wound elements possessed good performance stability and were suitable for single-pass seawater desalination.