Hello, this is Mai. I'm Vietnamese living in Perugia with residence permit validate

Mai, if you go to HK and Mainland China for tourism purpose, you should apply for two separate tourist visas for both places.
As for HK, you need to provide the filled-out application form, a passport-style photo, copy of your passport, proof of financial support, flight itinerary, hotel reservation and travel plan.
As for mainland China, you need to provide your passport and copy of its data page, the application form, a passport-style photo, air tickets and hotel reservation.
Next, submit two applications to the embassy of China.