A pressure gauge comprising: a hollow tube which is transparent and is formed in a cylinder shape, and the hollow tube including an accommodation chamber, a connector fixed on a center of an outer side of a first distal segment of the hollow tube and having a conduit which communicates with the accommodation chamber of the hollow tube, a display unit mounted on an outer wall of the hollow tube adjacent to the first distal segment and having at least one scale graduation to indicate a pressure value of an air compressor connected thereto; a drive element including a protection unit and being accommodated in the hollow tube so as to move linearly after being pushed by compressed airs of the air compressor, such that the pressure value is indicated by using a length of movement of the drive element, the drive element including a first open segment formed on a first end of the drive element, a second distal segment formed on a second end of the drive element, a receiving portion defined in the drive element, a hollow extension extending out of the first open segment from a center of a bottom of the receiving portion of the second distal segment, and a protrusion formed on an inner wall of the hollow extension and having an air channel; an anti-leak spring received in the hollow extension of the drive element, wherein a first end of the anti-leak spring abuts against the protrusion, and a second end of the anti-leak spring contacts with the protection unit; a resilient element received in the receiving portion of the drive element and fitted on the hollow extension; a cap including a seat extending from a center of an interior of the cap, a push bolt extending from a top of the seat and formed in a cross-shaped column shape, and multiple passages defined on an outer wall of the cap, wherein an end of the resilient element contacts with the cap; wherein the accommodation chamber of the hollow tube has a first fixing section and a second fixing section, a diameter of which is different from that of the first fixing section, the hollow tube further includes a surround section defined between the first fixing section and the second fixing section, and the hollow tube includes at least one discharge orifice, defined on the hollow tube. a hollow tube which is transparent and is formed in a cylinder shape, and the hollow tube including an accommodation chamber, a connector fixed on a center of an outer side of a first distal segment of the hollow tube and having a conduit which communicates with the accommodation chamber of the hollow tube, a display unit mounted on an outer wall of the hollow tube adjacent to the first distal segment and having at least one scale graduation to indicate a pressure value of an air compressor connected thereto; a drive element including a protection unit and being accommodated in the hollow tube so as to move linearly after being pushed by compressed airs of the air compressor, such that the pressure value is indicated by using a length of movement of the drive element, the drive element including a first open segment formed on a first end of the drive element, a second distal segment formed on a second end of the drive element, a receiving portion defined in the drive element, a hollow extension extending out of the first open segment from a center of a bottom of the receiving portion of the second distal segment, and a protrusion formed on an inner wall of the hollow extension and having an air channel; an anti-leak spring received in the hollow extension of the drive element, wherein a first end of the anti-leak spring abuts against the protrusion, and a second end of the anti-leak spring contacts with the protection unit; a resilient element received in the receiving portion of the drive element and fitted on the hollow extension; a cap including a seat extending from a center of an interior of the cap, a push bolt extending from a top of the seat and formed in a cross-shaped column shape, and multiple passages defined on an outer wall of the cap, wherein an end of the resilient element contacts with the cap; wherein the accommodation chamber of the hollow tube has a first fixing section and a second fixing section, a diameter of which is different from that of the first fixing section, the hollow tube further includes a surround section defined between the first fixing section and the second fixing section, and the hollow tube includes at least one discharge orifice, defined on the hollow tube.