1. A chatting system for a virtual pet, comprising: a pet client device including a processor coupled to a memory storing instructions for execution by the processor receiving a natural language sentence of a pet master and sending the natural language sentence to a virtual pet server device including a processor coupled to a memory storing instructions for execution by the processor; the virtual pet server device forwarding the natural language sentence to a question and answer server device including a processor coupled to a memory storing instructions for execution by the processor, and return a natural language response to the pet client device; the question and answer server device processing natural language understanding on the natural language sentence; obtaining language characteristics of the pet master and save the language characteristics of the pet master into a pet master language information base; generating the natural language response according to a natural language understanding result and the saved language characteristics of the pet master; and returning the natural language response to the virtual pet server device; wherein the language characteristics of the pet master include response habits commonly used by a user for responding to a certain natural language; the question and answer server device further adjusting the language characteristics of the pet master according to the natural language understanding result, history chatting records of the pet master, and the saved language characteristics of the pet master, and save the adjusted language characteristics of the pet master into the pet master language information base.