Abstract: For the improvement of loading technology of light oil products in railway transportation, the author makes a detailed introduction on the loading device of large crane sealing position under liquid which has being developed and brought into use more recently in those fields of structure, configuration, function and character. This device can reduse the proportion of light oil loss as low as 1.038‰, the maximum static potential oi loading product as low as 5 to 10 times as compared with other same type devices in China, and the monitoring value of hydrocarbon density in loading environment as low as 3 442 times as compared with the loading method of small crane spreading position above liquid. It has been proved practically in recent years that this device has such advantages as reasonable design, simply operation, sa ic and reliable program controlled system, smooth loading, high level of automation and remark able econcmic beneiit.