In this paper, the processes of water absorption expansion and water loss contraction of expansive soil are equivalently simulated by FLAC3D thermal fieldstress field coupling method and expansive coefficients setting, so as to analyze the influence of the expansive soil on the shallowburied twintube metro tunnel structure in expansive soil and optimize the construction parameters. Some conclusions are drawn as follows: 1) The comparison results between simulation method and field test show the rationality and feasibility of the simulation method. 2) When the clear distance between two tunnels is larger than 1.5 times tunnel diameter, the maximum ground surface settlement is 28.82 mm and the internal force of lining structure increases by less than 20%; the plastic zones of the central column of the two tunnels are not connected. 3) When the distance between two tunnel working faces is larger than 40 m, the maximum ground surface settlement is 30 mm and the crown top settlement increases by 10%; when the distance between two tunnel working faces is larger than 30 m, the plastic zones of the central column of the two tunnels are not connected. 4) It is suggested that the clear distance between two tunnels of the twintube tunnel should be larger than 1.5 times tunnel diameter; and the distance between two tunnel working faces should be larger than 40 m.