hello, i will be in Beijing can i know if there is airline to Aksu City?

I'm afraid there is no direct flight for both routes.
Thus Urumqi is a must transference destinations. Your route shoule be:
Beijing - Urumqi - Aksu - Urumqi - Xian
By the way, you can turn to company to book the air for you and arrange the specific transference things. If you want to book the flight ticket, the website may help you a lot.
https://www.travelchinaguide.com/china-flights/