The invention discloses a treatment method and device for a gas compressor communicating type contraction joint casing. The wall face of the gas compressor casing is provided with a plurality of dispersed contraction joints in the circumferential direction, and the joint depth direction is in the radial direction of a gas compressor. The sectional area of the contraction joints increases gradually in the axial direction, and the ratio of the rear end width to the front end width of the contraction joints is lowered gradually in the radial direction. Meanwhile, the sectional area of the rear portions of the contraction joints decreases gradually in the radial direction, and the sectional area of the front portions of the contraction joints increases gradually. Connection channels are formed between the rear portions of all the contraction joints, and thus the dispersed contraction joints communicate with one another. After accelerated in radial and axial contraction runners in the joints, sub-sound gas flow entering the contraction joints from the downstream parts of blade channels is jetted into the blade channels again from the upstream parts, and low-energy leakage flow at the blade tops can be blown away. Fluid in all the contraction joints can be exchanged through the connection channels, the backflow quantity in the contraction joints in different positions can be adjusted automatically according to the circumferential pressure distribution at the blade tops, thus blocking of different circumferential positions can be reduced effectively, and the stable work range of the gas compressor is increased.