Abstract: In order to investigate the characteristics and causes of persistent heaving of tunnel floor in red-bed mud? stone with complex geo-stress, taking a specific tunnel as the research subject, this paper carries out a statistic analysis on the deformation characteristics of the tunnel floor heaving through various methods such as long-term deformation monitoring, groundwater level monitoring, and surrounding rock displacement monitoring at the tunnel bottom. And it studies the respective factors that may lead to tunnel floor heaving through the combined assistance of different approaches such as analysis of drilling core samples, geo-stress test, surrounding rock swelling force test,rock creep test and numerical simulation analysis. The results show that governed by the near-horizontal bedded mudstone and complex geo-stress, some sections of the tunnel display three features, i.e. "non-convergence" of the floor heaving time, "uncontinued" of floor heave sections, and "uneven" of heaving degree. The occurrence of the tunnel surrounding rocks is nearly horizontal, with a lithology of silty mudstone, so it is a soft rock that does not meet the classification criteria for swelling rock, with medium-low creep characteristics, and the geo-stress field at the tunnel site is mainly horizontal tectonic stress, with the horizontal stress between 9.5 ~ 13.73 MPa. As the tunnel is excavated, the local stress concentration leads to surrounding rock creep, and when the creep generates excessive deformation pressure, the parts of the inverted arch would enter into a plastic state, and thus inducing the tunnel floor heave.