The negative pressure weighing booth is a kind of purification equipment, its pressure in working area is lower than outside. It is mainly used for weighing materials such as drugs or activated carbon, and four levels of protection in the process of sub-packaging: materials are protected from pollution by personnel and environment, the environment is protected from pollution by materials and dust, and operators are protected from pollution by materials and dusts. Its air flow pattern and pressure of the environment are not affected by on or off state of weighing booth. The equipment is widely used for weighing and sub-packaging in pharmaceutical, medicine and health and environmental protection.