A quasi-steady approach to high-speed train fluid-structure dynamics is presented for the issue of a linear wind shear with steady regions. Based on that approach, the dynamic performances of high-speed train are analyzed under different wind shear environments. It is concluded that the safety indexes become worse with the incremental of the train's running speed and the decrease of the linear wind shear time interval. The magnitude of the wheelset lateral force, derailment coefficient and wheel unloading are beyond the allowed values in some cases. Besides, the magnitude of the wheel rail vertical force is relative difficult to go beyond the allowed value. When the running speed of a train is larger than 300km/h, wheel unloading is chosen as the evaluation safety index; when the running speed of the train is less than 250km/h, wheelset lateral force and derailment coefficient are chosen as the evaluation safety indexes. Results show that the region of safety running speed in wind shear is smaller than that in traditional crosswind; viz. the running safety becomes worse in wind shear.