This study focuses on nonlinear behavior of aeroelasticity and dynamic elastic load of vertical tail on fighter aircraft in a state of transonic speed. A time domain coupled CFD/CSD strategy is introduced and a method of calculating elastic load is presented by using this strategy. The analysis is based on numerical results of flutter boundary of 0°sideslip angle under different mach numbers and unsteady aeroelastic load at 0.9 Mach、sideslip angle of 2°and 10°, and the effect of rudder on flutter is detected. Dynamic responses of inertial load and elastic load are also available.