IS THERE A SUBWAY LINE TO XIANYANGINTERNATIONAL AIRPORT FROM XIAN INTERNATIONAL CONVENTION CENTRE ?

No subway line connects the two destinations! And there is no metro station within walking distance to the convention center. Well then, I suggest you walk to Provincial Shooting Range (Sheng Shejichang) to take bus no. 722, 407 or 504 to get off at Xiaozhai! Then walk to the exit C or Xiaozhai metro station, near which you can find airport shuttle bus. Take that to the airport then! Well, your location is 4-4.5km to Xiaozhai, so you can also take a taxi to get there, at the cost of CNY10-12.