Reduced graphene oxide membranes (rGOMs) have been intensively studied for desalination and molecular sieving applications, benefiting from their selective and stable two-dimensional (2D) nanochannels. However, their performance is usually over-rated because of the limited understanding of nanowrinkles. In this study, we tuned 2D nanochannels and nanowrinkles in rGOMs to improve their performance and revealed the underlying role of nanowrinkles for water and salt separation. A good trade-off between water permeance (1.05 LMH/bar) and NaCl rejection (83%) was obtained in rGOMs thermally treated in air (Air-rGO), compared with their counterparts synthesized via thermal treatment in vacuum (Va-rGO) and HI vapor reduction (HI-rGO). Instead of the narrow and impermeable 2D nanochannels in Va-rGO and HI-rGO, 5-10 nm-sized nanowrinkles were evident to transport water and salts without selectivity, leading to the low water permeance and NaCl rejection. For Air-rGO membranes, however, the smaller and fewer nanowrinkles retarded the NaCl transfer and the slightly narrowed 2D nanochannels maintained the fast water flow, contributing to the high NaCl rejection and water permeance, respectively. This study provides new insights into the mass transport mechanism in nanowrinkles of rGOMs and advances the design of 2D membranes for desalination, molecular/ionic sieving, and other environmental applications.