Abstract: The sloping ground may suffer from lateral spreading due to earthquake-induced soil softening or liquefaction, and this deformation is usually relatively limited in the gentle sloping ground. However, several hundred meters of lateral deformation were observed in gentle sloping ground within 3° during the 2018 Sulawesi Earthquake. This phenomenon can not be explained through the observations from the existing model tests and numerical computations, where only the shear wave ground motion is considered. The numerical simulations using the smoothed Particle Hydrodynamics (SPH) method are conducted to show that Rayleigh wave input plays an important role in lateral spreading in the gentle sloping ground. The ground soil is simulated through the Herschel Bulkley Papanastasiou (HBP) rheology constitutive model, the Rayleigh wave is input using the dynamic boundary particles (DBP) boundary condition, and the geographic information system (GIS) is utilized for 3D spatial modeling. The deformation characteristics of the gentle sloping ground under the Rayleigh wave and shear wave are computed and compared, revealing the cause of the observed large deformation of Balaroa landslide in 2018 Sulawesi Earthquake.