The present invention discloses a method and a device for generating a phone bill, which is applied to a charging system in the communication field, wherein the method comprises a preprocessing process and a process of combining phone bills, wherein in the preprocessing process, the charging system uses multiple threads for preprocessing a plurality of service logs simultaneously, and each service log is preprocessed to generate one or more intermediate phone bills, wherein information in the service log is converted into information required for the intermediate phone bills when performing preprocessing, and a single thread is used for processing in the process of combining phone bills to generate required phone bills one by one, and during each process of generating a phone bill, the charging system collects and combines the intermediate phone bills required for generating present phone bill, accomplishes encoding record serial numbers and file serial numbers, and generates one phone bill. The present invention reduces the processing complexity while guaranteeing the processing capacity of the system.