A tire pressure gauge includes a holder, an air intake seat, and a detection device coupled with the air intake seat. The holder and air intake seat have respectively a first positioning ring and a second positioning ring. A fastening and unfastening tool of the tire pressure gauge includes an outer barrel and an inner barrel held in the outer barrel. The outer barrel has a first anchor portion to latch the first positioning ring. The inner barrel has a second anchor portion to latch the second positioning ring. The outer barrel and inner barrel respectively drive the holder and air intake seat to be fastened to an air nozzle of a vehicle tire, and the holder and air intake seat are butted tightly to allow the tire pressure gauge to be securely installed on the air nozzle of any type of vehicles through the fastening and unfastening tool.