Hi Duy,
For your scenario you need to use the ContentPanels of the TabItems. When selecting the tabs, the RadProgressBar control should be removed from the ContentPanel.Controls collection of the previously selected tab and should be added to the ContentPanel.Controls collection of the newly selected tab.
I am attaching a sample project to demonstrate this approach. If you have additional questions, feel free to contact me.
Kind regards,
Nikolay
the Telerik team