I have applied for a travel permit and found my passport again. Can I buy a plane ticket to return to China with the original passport?

You can't. If the passport is lost abroad, but the original passport has been found, then under normal circumstances, the original passport can no longer be used normally, because the travel document after the passport is lost is a new identity certificate and the original passport has expired. If you lose your passport abroad, you need to call the local immigration bureau or embassy for help immediately. When handling travel documents, you need to provide relevant supporting documents, such as alarm certificates and air tickets. After you get a travel document, you can use it to buy a plane ticket back to China. Even if you find the original passport, you still need to use it to travel, because the travel document is a new identity certificate and the original passport has expired. If the original passport has information such as visa or important visa records, you can try to transfer the relevant information to the new passport, but the specific operation needs to be determined according to the regulations of different countries and regions.