The invention discloses a precise inner hexagon machining lathe for a valve element of a pressure valve and a machining process of the precise inner hexagon machining lathe. The precise inner hexagon machining lathe comprises an equipment base, a moving device is arranged on the left side of the top of the equipment base, a height adjusting mechanism is arranged on the right side of the top of the equipment base, a transverse moving mechanism is arranged on the top of the left side of the height adjusting mechanism, and a broaching tool adjusting mechanism is arranged at the bottom of the transverse moving mechanism. In actual use, lathe machining is adopted, a 120-degree-angle tool is customized, a main shaft is locked, and movement of a tool turret in the Z direction is utilized, so that one angle in a hexagon can be broached, the rest five angles are machined in sequence after the main shaft uniformly rotates by 60 degrees, and therefore, by means of the machining mode, the broaching amount each time is about 0.05 mm, the machining precision of the hexagon can be met, the machined surface is flat and smooth, no stamping stress is generated, the deformation of the size of the inner hexagon after heat treatment can be controlled more easily, circulation of parts is reduced, and the machining efficiency is improved.