A negative pressure gauge includes a body and a multi-stage positioning means. The body is provided with an airflow passage. The multi-stage positioning means includes a rotary piece and a cover plate. The rotary piece is pivotally connected to the body and is provided with positioning recesses and venting troughs. The cover plate covers the rotary piece and is fixedly connected to the body. The cover plate extends to form a positioning protrusion corresponding to the positioning recesses. When the rotary piece rotates with respect to the cover plate, the positioning recesses allow the positioning protrusion to be selectively positioned therein and control the communication or obstruction between the venting troughs and the airflow passage.