The invention provides a cloud system, a cloud public service system and a mutual access method for the cloud system. The cloud public service system includes: at least one public service mainframe which supports a second network protocol; a cloud virtual switch which includes: a switching apparatus which is configured to, based on the only identifier of the virtual private cloud which conducts mutual access with the public service mainframe, convert a first packet transmitted to the public service mainframe by a virtual private cloud from the message format of a first network protocol to the message format of the second network protocol; and/or convert a second packet transmitted to the virtual private cloud by the public service mainframe from the message format of the second network protocol to the message format of the first network protocol, wherein the source destination address in the message format of the second network protocol is longer than that of the first network protocol. According to the invention, the cloud system, the cloud public service system and the mutual access method for the cloud system can realize efficient mutual access.