Abstract: Based on a highway tunnel in loess, the triaxial tests under different moisture contents of undisturbed Q₂ loess are conducted to obtain the physical and mechanical parameters, and the numerical method is used to analyze the variation laws of surrounding earth pressure(SEP)under the infiltration of surface water or rising of underground water level.The modified methods for SEP are put forward by considering the effects of moisture content.The results show that:(1)With the increase of rising height of underground water level and the infiltration depth, the SEP exhibits a trend of increase, and the largest SEP ratio ψ_max=1.1~3.5, the largest surrounding earth convergence deformation ratio ζ_max=1.1~1.3.(2)The lower the initial moisture content of the loess stratum, the greater the maximum SEP ratio and convergence deformation ratio, and the more obvious the SEP amplification effect caused by water infiltration or rising of water level.(3)The shallower the buried depth of tunnel is, the more uneven the SEP distribution is, the more obvious the shape of "cat's ear" is, and the more evenly the SEP distribution is.(4)By introducing the SEP ratio, a semi-numerical and semi-empirical formula for calculating the SEP of the tunnel is put forward, and the amplification effect of SEP caused by the increase of moisture content of loess can be considered.