A tire pressure gauge which contains: a housing, a pressure measuring unit, and a tire-tread depth measuring unit. The tire-tread depth measuring unit includes a mounting assembly, a gear assembly, a hair spring, a covering lid, and a longitudinal post, such that the tire pressure gauge measures a tire pressure and a tire-tread depth. The tire-tread depth measuring unit indicates a number of the tire-tread depth by using a pointer, after a measurement stem of the longitudinal post is inserted into a tread slit of a tire, and a longitudinal movement of the longitudinal post is transformed into circumference rotation data through the gear assembly, thus indicating the number of the tire-tread depth on a numerical display panel clearly. Preferably, a probe and the measurement stem of the longitudinal post inserted into the tread slit are driven by the hair spring to return zero state.