Online monitoring of oil chromatography is a widely used means of monitoring. However, because the perception layer protocol and internet of things (IoT) model of the current oil chromatography online monitoring system have not yet been unified, difficult data interaction enables the oil chromatography system to operate independently. It also realizes data sharing with other subsystems on the power transmission and transformation side. A data access method for an oil chromatography online monitoring system is proposed to realize plug-and-play. First, the overall architecture of the oil chromatography system data access IoT management platform under the smart IoT framework is analyzed. Then the system data transmission process is clarified. Then, a unified IoT model based on a State Grid common information model (SG-CIM) is constructed. A communication mode is proposed between the oil chromatogram system acquisition terminal and the edge IoT agent. This is based on local communication and the interaction mode between type III edge IoT agent and IoT management platform based on message queuing telemetry transport (MQTT) protocol. Then the system has a unified IoT model and communication protocol in the process of data transmission. Thus, the data of the oil chromatography online monitoring system is connected to the unified IoT management platform. Finally, taking the actual operation of the oil chromatography online monitoring system in a province as an example, the data uploaded to the IoT management platform is compared with the original data in the oil chromatography online monitoring system. This is to verify the timeliness and integrity of the access data, so as to verify the feasibility of the proposed access method. The proposed method has important reference significance for realizing the data sharing and linkage of the main equipment at the power transmission and transformation side. It also can help improve the perception of the operational state of the main equipment at the power transmission and transformation side. This work is supported by the National Natural Science Foundation of China (No. 51807180).