The present invention relates to a fluid compressor comprising: a driving module comprising a driving motor embedded in a motor case; and a compression module comprising a rotor, which is rotatably driven by a driving motor and which has a plurality of variable blades radially provided along the outer peripheral surface thereof, a rotor housing for encompassing the rotor, and a cover of the rotor, for closing the rotor housing, wherein the compression modules are stacked and airtight to block contact between fluid passing through the compression module and air outside the compression module, so that the fluid flowing into any one compression module sequentially passes through the remaining compression modules. The rotary shafts provided in each center of the rotors are connected a shaft coupler. The present invention simultaneously achieves a high-efficiency compression ratio and reduces noise caused by the excessive velocity of any compression module.