In this paper, the energy band structure and topological surface state of type Ⅱ Dirac semimetal PtTe₂ are calculated based on first-principle calculation. A layered PtTe₂ is prepared by the mechanical lift-off approach, and a metal-PtTe₂-metal field effect transistor is fabricated based on micro-nano processing. The photocurrent response of a field-effect transistor device based on type Ⅱ Dirac semimetal PtTe₂ in terahertz region is studied. The device has an obvious photoresponse to terahertz, with a responsivity of 3.85 A/W and an equivalent noise power of about 4.81 pW·Hz^-1/2. It shows a wide range of application prospects in low-energy bands, especially terahertz bands.