Hello, is it convenient to travel this way Beijing--Datong--Taiyuan—Pingyao--Beijing?

Hi, I suggest you adjust that like this:
Beijing - Datong - Pingyao - TY city - Beijing

Generally, trains can be fuly used for all your journeys. From Beijing to Datong, you can take a train to travelo within around 6h. Then to Pingyao, the train is also recommended. To TY, you can take either bus or train to. After traveling back to Beijing, the high-speed train can take you there in around 3.5h.