The principle is that the phase angle of the moving scroll and the fixed scroll is 180 when they are installed, so that the two scrolls are meshed with each other to form a series of crescent scrolls. The movable scroll is driven by a crankshaft with small eccentricity, which makes it rotate around the axis of the fixed scroll. In addition, a coupling mechanism is used behind the orbiting scroll to ensure the relative translation between the orbiting scroll and the fixed scroll. During this translation process, the refrigerant vapor is sucked into the crescent-shaped working volume from the outer edge of the scroll, and the working volume gradually moves toward the center and decreases, so that the refrigerant vapor is compressed. When the gas pressure is higher than the pressure outside the exhaust valve, the exhaust valve opens. Finally, it is discharged axially through the central exhaust port, thus completing the whole cycle of inhalation, compression and exhaust.