The invention discloses an online charging engine, a real-time charge off engine, and an online charging method and 
system. The online charging method comprises the following steps: receiving an online charging request, obtaining 
current user state information corresponding to a terminal identifier of a terminal, and performing 
authentication on a service request according to the 
current user state information, wherein the 
current user state information is 
user state information after the online charging 
processing of the previous online charging request of the terminal is terminated, and an 
authentication result of the service request is sent to a service 
network element. By adoption of the online charging method, service 
authentication and real-time charge off are 
asynchronous processing procedures, the 
response period of the service authentication is shortened, the 
retention rate of the online charging flow of the user is improved, the working load of the 
online charging system on service peaks is reduced, and thus the technical problem of large working load of the 
online charging system on service peaks, relatively low 
retention rate of the online charging flow of the user and influence to the service 
perception of the user on the flow service in the prior art are solved.