Organic solvent nanofiltration (OSN) technique provides a broad prospective to protect the environment and save energy, but it faces certain challenges due to the relatively weak tolerance of OSN membranes under very harsh organic solutions and their relatively poor separation performance. A new class of sandwich-like thin-film nanocomposite (TFN) OSN membranes that can cope with these challenges have been fabricated via interfacial polymerization (IP) on porous PI substrate surfaces modified by crosslinked graphene oxide (cGO) nanosheets. The hydrophilicity and roughness of these substrate surfaces, as well as the subsequent IP reaction, were successfully manipulated and optimized by the ultrathin layer of the covalent, immobilized cGO nanosheets. The newly formed TFN OSN membranes possessed an ultra-smooth, hydrophilic, and defect-free polyamide barrier layer with ultralow average roughness (only about 2 nm), ultrathin thickness (about 15 nm), ultrahigh crosslinking degree (about 98.64%), high separation performance (rejection greater than 99.4% for rhodamine B (RDB, 479 Da) and ethanol permeance of 41.47 L m⁻² h⁻¹ MPa⁻¹), and superb solvent resistance (rejection higher than 98% for RDB after being immersed in pure DMF at 80 °C for more than 160 days), suggesting their promising potential in the application of organic solution separation and purification.