The invention relates to a data transmission method and device for on-line monitoring device quality simulation testing. The method includes the following steps that: S1, a status access controller generates corresponding messages according to output data of an on-line monitoring device, and sends out the messages; S2, the messages sent by the status access controller are received, and are analyzed; and S3, whether the messages accord with the I2 protocol is jugged according to analysis results, if the messages accord with the I2 protocol, the messages are stored, if the messages do not accord with the I2 protocol, protocol error information is returned to the status access controller. Compared with the prior art, and according to the method of the invention, protocol analysis is performed on the messages sent by the status access controller, and when the messages do not accord with the I2 protocol, the protocol error information is fed back to the status access controller timely, and therefore, pre-verification can be performed on messages entering a testing device, and a specially-assigned person is not needed to perform protocol accordance judgment, and therefore, labor force can be saved.