<p>This study demonstrated a simulation of bidispersed granular column collapse using the Discrete Element Method (DEM) and an elastoplastic model based on Smoothed Particle Hydrodynamics (SPH). The present simulation model was developed to solve the deformation of a mixed layer of a small-scale granular material, such as sand, and a large-scale material, such as gravel. In the present model, the behavior of a large granular material was tracked using the DEM, and a small granular material was treated as a continuum on the basis of an elastoplastic constitutive law in an SPH framework. The model was validated by comparing its simulation data with the experimental results of previous studies. First, in the simulation of the collapse of a monodispersed granular column for each granular material size, some parameters were tuned. Thereafter, five simulation cases with varying mixture arrangements of the two granular materials were conducted. The position of the center of gravity of each material in the final deposit after collapse was investigated. The calculated results well agreed with the experimental results.</p>