  In this paper, we investigate the quasiparticle scattering interference(QPI)
in the nematic phase of iron pnictides, based on the magnetic and orbital
scenarios of nematicity, respectively. In the spin density wave(SDW) state, the
QPI pattern exhibits a dimer structure in the energy region of the SDW gap,
with its orientation along the ferromagnetic direction of the SDW order. When
the energy is increased to be near the Fermi level, it exhibits two sets of
dimers along the same direction. The dimer structure of the QPI patterns
persists with the decrease of the SDW correlation length in the magnetic driven
nematic phase, although it tends to merge together for the scattering patterns
with energies close to the Fermi level. While in the orbital scenario, the QPI
patterns exhibit a dimer structure in a wide energy region. It undergoes a
{\pi}/2 rotation with the increasing of energy, which is associated with the
inequivalent energies of the two Dirac nodes induced by the orbital order.
These distinct features may be used to probe or distinguish two kinds of
scenarios of the nemeticity.
