Even though the hyperbolic phonon polaritons (HPPs) in hexagonal boron nitride (hBN) have been extensively studied, the HPPs in ultrathin hBN have not been fully considered and remain elusive. In this work, the HPPs in ultrathin hBN sheets are numerically studied. The dispersion relation and distribution of electric field are calculated to confirm the excitation of HPPs. Besides, the coupling effect between HPPs of two ultrathin hBN sheets are investigated. When the distance between two hBN sheets are smaller than the propagation length of the HPPs in the air, the HPPs can be strongly coupled. Therefore, the photon tunneling probability can be greatly enhanced. The splitting of the HPPs is similar to that of the surface waves, and such phenomenon is well explained in this work. The results show that the HPPs in ultrathin hyperbolic films share some characteristics with surface waves, and thus they should be clearly identified by investigating the dispersion relation and field profile. We believe that this work will deepen our understanding of the HPPs in ultrathin hyperbolic materials. In addition, the knowledge about the HPPs will help us understand the near-field radiative heat transfer between hyperbolic materials.