Due to the unstable loading conditions in complex geological environment, shield boring may face such problems as uneven pressure on the cutterhead, vibration and deformation of cutterhead and abnormal damage of cutting tools. In the paper, the stress and strain conditions of the cutterhead under unstable loading conditions are analyzed by means of finite element method and on basis of the actual parameters of the cutterhead and strata in the site. In the end, the stressstrain conditions of the cutterhead of the shield under the unstable loading conditions in the mentioned strata are obtained and the reliability of the cutterhead design is ensured. 