In Italy, how can I return to China without a passport and residence?

It depends on the type of visa you have. If it is a multiple-entry visa, you can go back to China first and then to Italy. If it is a single entry visa, you can't go back to Italy.

Multiple entry visa means that ordinary visa can be used multiple times (within the time limit). Visa is the annotation and seal of the sovereign organ of a country on the passport or other travel documents held by its own or foreign citizens to show that they are allowed to enter or leave the country or pass through it. It can also be said that it is an endorsement certificate issued to them. Generally speaking, a visa is a document issued by a country's entry-exit administration (such as immigration bureau or its embassy or consulate abroad) to approve the entry of foreign citizens.