Disclosed are a wafer carrier that keeps wafers under a constant pressure, at any preset value below or above the atmospheric pressure, to prevent wafer contaminations arising from atmospheric exposure in conventional wafer carriers, and also, a wafer transport system and method utilizing the same wafer carrier. The wafer carrier charged with a preset carrier pressure is transported and docked with an airlock of a wafer processing tool comprising the airlock, a vacuum transfer module, and a process chamber. The airlock adjusts, by a gas pump, inner pressure to equate successively with, first, the carrier pressure before opening the carrier door, and next, the vacuum transfer module pressure before opening the latter's door. The wafers are then transferred into the process chamber. After processing, the wafers are transferred back into the wafer carrier and charged with the preset carrier pressure before undocked and transported to the next wafer processing tool.