Is there a long distance bus from dunhuang to Xian i can take??

The distance is about 1074 mi (1729 kilometers), it’s too far, so no direct bus service is available. But there are direct flight and train.
If by flight, it would take about 2 hours to reach Xianyang Airport.
If by train, you can take train K592 to reach directly. The duration is about 24 hours. Ticket price for soft sleeper is CNY582, and for hard sleeper is CNY377.