To study effects of the asymmetry during construction and the bias effect caused by natural terrain on the safety of double-arch tunnels under adverse geological conditions and rainy sections, this paper takes Leijiatai biased double-arch tunnel in central-western of Hunan Province as engineering background. Based on the seepage-stress coupling analysis theory, the excavation process of bias multi-arch tunnel is simulated by using the finite element analysis software MIDAS/GTS. Combined with the monitoring data during construction, the deformation characteristics of surrounding rocks in the double-arch tunnel subjected to biased pressure are analyzed, the influence of biased pressure on the stability of double-arch tunnel is further discussed. The results of numerical simulation and of monitoring during construction are analyzed and compared, which indicate that the connection between the upper left step of the left tunnel and the middle partition wall and the arch of the right hole are relatively weak positions during the construction process of bias double-arch tunnel. The mechanical characteristics of the double-arch tunnel structure are also obtained to provide a reference for the design and construction of analogous projects.