The problems of load uncertainty and difficult prediction of dynamic characteristics of the cutterhead system of TBM induced by the uncertainty of the working conditions during fullface hard rock TBM tunneling need to be solved. Hence, a dynamic analysis method for uncertainty of working condition is put forward. Firstly, the equivalent of 4 typical working conditions is carried out, the equivalent loads of different working conditions are expressed by interval theory, and the uncertainty of working condition is transformed into the uncertainty of load. And then the multidegree freedom coupling dynamic model of the cutterhead is established by the lumped mass method, the multidegree freedom coupling dynamic model under uncertain working conditions is obtained based on the interval uncertain load, and the dynamic response under uncertain working condition is calculated. Finally, the abovementioned method is verified by field test data. The study results show that: (1) The difference of working conditions should be fully considered during TBM design. (2) The stability of the cutterhead system has been increased with the increase of the cutterhead block. (3) The cutterhead system has a better vibration stability when the drive gear is evenly distributed.