Abstract: In order to improve precision of automated greenhouse gas sampling in the field, the differences between direct tube gas sampling and pre-vacuum gas sampling in the field automated continuous greenhouse gases measurement system were compared. The results show that, in comparison with direct sampling, the pre-vacuum sampling can dramatically decrease gas sampling volume, shorten sampling time, and minish the difference of gas sample and the source, and thus improve sampling precision. So the pre-vacuum sampling is much better than direct sampling in field automated greenhouse gases measurement system.