Data transmission method and system

The invention relates to a data transmission method and system. The method comprises the steps that an industrial control adapter serving as a slave node detects whether a data reporting condition is met or not; wherein data transmission is carried out between the industrial control adapter and the server through a modbus master-slave protocol, and the server is used as a master node; and when the data reporting condition is met, the industrial control adapter automatically transmits the data content to the server. According to the technical scheme, the data reporting condition is detected on the industrial control adapter side serving as the slave node, and the data content is automatically transmitted to the server when the data reporting condition is detected to be met, so that the scheme that the slave device actively transmits data with the master device is realized, and equivalently, the data transmission between the slave device and the master device is realized under the modbus master-slave protocol.