In this work, a simple method was proposed to fabricate robust, breathable and waterproof polymer nanofiber membranes. In a typical process, polyamide-6 (PA-6) electrospun membranes were immersed into polyurethane (PU)/DMF solutions for 24 h, and then taken out and dried. SEM results showed that PA-6 nanofibers in the membranes adhered to each other at the inter-fiber junction points. Moreover, the nanofibers were covered by a thin layer of PU, which was also proved by FTIR results. The DSC and WAXD results suggested that the PU had interacted with the PA-6 at molecular level. Through adhesion bonding, the PA-6 nanofiber membrane was interlinked into a huge network, leading to drastically increment in tensile strength of these membranes (357% that of the original value). Moreover, the PA-6 membranes achieved good waterproof ability after the PU solution treatment. The water contact angle was 135.8°, comparable to that of the poly(vinylidene fluoride) (PVDF) electrospun membrane or fluorinated PU/PU coelectrospun membrane. Interestingly, the PU solution treated PA-6 membranes preserved good breathability. It is a facile and scalable approach to fabricate the robust, breathable and waterproof polymer nanofiber membranes.