Do I need a visa to China?

Anutka, you are almost certainly eligible for 24 hour visa free transit.

Anyway, I hope you don't have any additional landings within mainland China and that your itinerary is:

Yekaterinburg - Xi'an - Bangkok

And for your journey back:

Bangkok - Xi'an - Yekaterinburg

If the above itinerary is exactly your one, you will be eligible for 24 hour visa free transit during your first stop in Xi'an and for 24 or 144 hour visa free transit during your second stops in Xi'an in direct relation to the length of your entire transit time that you will spend in Xi'an area.

You should print out your flight tickets and have those printouts with you. Also, you will declare in Yekaterinburg that you will travel to Bangkok via Xi'an using 24 hour visa free transit. After a short inspection of your tickets, you will be allowed to board the plane.

Upon your arrival in Xi'an, you will immediately apply for a temporary entry permit at 24 hour visa free transit counter. This permit will be definitely granted to you to allow you to collect your luggage and also to perform your check-in for Bangkok flight. Everything mentioned will be exactly in the opposite direction.

By the way, Air Asia is fine for visa free transit, but you should arrive at Bangkok Don Mueang airport well in advance to perform your check-in and to ask for a superior in case that a member of the staff does not understand your intentions for visa free transit through Xi'an.

I would like if you could confirm your flights. Thanks.