The influence of groundwater on load distribution of shield tunnel and ground deformation of Chengdu Metro Line No. 2 is analyzed microscopically by means of particle flow cate in two dimensions(PFC2D) method. The soil stress and water stress during shield tunneling and after shield passing are studied. The study results show that: 1) The stress on tunnel lining structure considering groundwater is smaller than that without considering groundwater; and the higher the water level is, the smaller the stress on tunnel lining stress is. 2) The stress redistribution of surrounding rocks is affected by groundwater after shield passing; and the arch crown is affected mostly and the arch shoulder is affected minimally. 3) The loose zone above tunnel arch crown bears the soil load; as a result, the effective stress on the tunnel is decreased and the deformation of the tunnel can be decreased.