The embodiment of the invention provides a communication method and system, and relates to the technical field of communication. A client and a server transmission messages, and transmission flow is compressed by defining the formation format of the messages. The method comprises the following steps: the client sends a request message to the server; the server receives the communication method and system and returns a response message to the client according to the request message; and the client receives the response message returned by the server, wherein the message consists of a start marking bit, a message header and a message body, the start marking bit is expressed by a byte, the message header comprises a message type and a message sequence number, the message type is expressed by previous 4 bits of a byte, the message body comprises a starting byte and a message field, and the message field is expressed by a numerical value or a numerical value index. The technical scheme provided by the embodiment of the invention is applicable to the message transmission process between the client and a public traffic monitoring center server in a public transport system.