The oil-free screw air compressor belongs to a micro reciprocating piston compressor. The motor drives a symmetrical distributed crank rocker mechanical structure with a single axis. The main motion pair is a piston ring, and the auxiliary motion pair is an aluminum alloy cylindrical surface. The motion pairs are self lubricated with the piston ring without adding any lubricant. The moving pairs and piston rings are self lubricated without adding any lubricant. The reciprocating movement of the compressor through the crank rocker makes the cylinder volume change periodically, and the cylinder volume has two opposite changes in one cycle of motor operation. When the positive direction is the expansion direction of the cylinder volume, the cylinder volume is vacuum, the atmospheric pressure is greater than the air pressure in the cylinder, and the air enters the cylinder through the air valve. This is the suction process: when the reverse direction is the volume reduction direction, the gas entering the cylinder is compressed, and the pressure in the volume increases rapidly. When the atmospheric pressure is greater than the atmospheric pressure, the exhaust valve is opened, and this is the exhaust process. The structural arrangement of single shaft and double cylinders makes the gas flow of the compressor twice that of the single cylinder when the rated speed is fixed, and the vibration noise generated by the single cylinder compressor is well solved, making the overall structure more compact.