Seems there is no good shops at the airport. But, you could shop at these department stores around the Bell Tower after you arrive there by shuttle bus. There are some sports clothes shops such as Nike and Ads just at the bus stop. Or, a little walking back to Inn Time or ahead to Kaiyuan Shopping Mall, both of which will be closed at 21:30. The price of winter clothes varies greatly in terms of material and brand, from several hundred RMB to over one thousand. On the other hand, you could purchase some cheaper ones the next day at Xiaozhai commercial area not far from Xi'an Hotel.

thanks a lot Mr Meng!!! really appreciate ur help