Analysis on the flutter characteristics of Ttails is complicated because of their special structure and aerodynamic configuration. The T empennage is fixed on the afterbody, and in a structure finite element model, this can be represented by connecting the Ttails and the main beam. To study the influences of stiffness variations of tail mainbeam on flutter characteristics, the empennage of a Ttail aircraft is studied according to its original stiffness, considering the change of vertical bending stiffness and torsional stiffness. And the corresponding characteristics of natural vibration and flutter are analyzed. Finally, the flutter characteristics of models with two variable of above stiffness (vertical bending stiffness and torsional stiffness) and one constant of the original value of either stiffness are analyzed. The results demonstrate that the influences of stiffness variations of tail mainbeam on bendingtorsioncoupled flutter of vertical tail are significant.