The invention relates to a continuous sampling and analyzing device used for loading / unloading LNG (
liquefied natural gas) and a using method, which are characterized in that the sampling and analyzing device comprises an LNG sampling probe, a gasification device, a main sampling pipeline, a 
BOG (boiled off gas) return device, an on-line analyzing device, a flow control device, a sample gas storage device, a sample steel 
bottle filling 
system and a 
control system, wherein the LNG sampling probe is connected with an inlet of the gasification device by an isolation shut-off valve and temperature detection element; an outlet of the gasification device is connected with the 
BOG return device by the main sampling pipeline and is also connected with the on-line analyzing device and the flow control device by the main sampling pipeline respectively; the flow control device is also connected with an inlet of the sample gas storage device; an outlet of the sample gas storage device is connected with the sample steel 
bottle filling 
system; the sample steel 
bottle filling 
system is also connected with a 
BOG main 
pipe; the isolation shut-off valve, the temperature detection element, the main sampling pipeline, the flow control device, the sample gas storage device and the sample steel bottle filling system are respectively electrically connected with the 
control system. The continuous sampling and analyzing device can be widely used in a facility used for analyzing an LNG component and calculating an LNG caloric value.