Water vapor in humid air and industrial gases needs to be removed for various applications such as air conditioning, foodstuffs storage, aviation and space flights. Membranes can remove water vapor from gas streams without involving phase change and regeneration. A robust and productive membrane is vital for water vapor removal but it is challenging to produce it. Here we present a defect-free thin film composite (TFC) polydimethylsiloxane (PDMS)/polyacrylonitrile (PAN) hollow fiber membrane with an ultrathin PDMS selective layer of about 260 nm. Different from previous works, the PAN substrate was spun at a high take-up speed of 60 m/min. It has an average of surface pore size of 5.6 nm and superior mechanical properties. After the optimal PDMS coating, the composite membrane shows a N-2 permeance of about 280 GPU, an O-2/N-2 selectivity of 2.2 and a water vapor permeance ranging from about 800 to 3700 GPU depending on operation conditions. In addition, the PDMS/PAN composite membrane has been tested for 48-hour outer door dehumidification and shown very stable and robust performance with a water vapor removal rate of 65% from the humid air. Besides, the PDMS/PAN composite membrane is not only able to efficiently dry the humid biogas but also upgrade its methane content simultaneously. Therefore, the newly developed TFC composite membrane has great potential for water vapor removal from humid air and various gas streams.