Negative pressure weighing room is a kind of local purification equipment used in pharmaceutical, microbial research and scientific experiments, which provides a vertical unidirectional air flow. Part of the clean air circulates in the work area and part is discharged to the nearby area, making the work area produce negative pressure. The dust and reagent weighing and packing in the equipment can control the spillover and rise of dust and reagent, prevent the dust and reagent from inhaling harm to human body, avoid the cross pollution of dust and reagent, and protect the external environment and indoor personnel safety.