The invention discloses an elastic longitudinal joint device used for shield tunnel segments in swelling soil areas. The longitudinal joint walls of the segments are provided with rubber belts covering all the longitudinal joint walls; the rubber belt at a sealing groove is positioned between a sealing groove wall and a sealing gasket; the thickness P of the rubber belt is determined by a formulashown in the description; and in the formula, P' is the thickness of the rubber belt compressed under the action of the axial force of a lining structure and is 3 to 8 mm; E2 is the elastic modulus of the rubber belt; N is the axial force acted on the lining structure; and A is the action area of the axial force, and A=bh, wherein b is the length of the longitudinal joint of each segment, and h is the thickness of the segment. The device can greatly reduce the equivalent stiffness of a lining so as to reduce the swelling force acted on the lining and guarantee the safety and reliability of shield tunnel structures built in the swelling soil areas; meanwhile, the device reduces the internal stress of the lining structure, effectively reduces the reinforcement of the lining, and has high waterproof property.