This study focuses on the main factor of regional difference in Altitudinal Dependency of Snow Depth (ADSD) and discusses the applicable range of snow cover estimation method with ADSD. We use the high-density surface observational data and a regional climate model in Niigata Prefecture. The estimation method with ADSD produces significant estimation error if the method is applied to broad areas. The high-density observational data show the regional difference of ADSD between windward and leeward areas with a coastal mountain. Numerical simulation reproduces these observational results. We evaluate mountain effects on the regional difference of ADSD using sensitivity experiments. In the sensitivity experiment, the altitude is changed from a mountain to a flat plain. The sensitivity experiment shows that the regional differences of ADSD are not simulated. The results indicate that the applicable range of the estimation method with ADSD is limited to a single slope and mountain. It should be noted that this method has a high probability of increasing the estimation error in complex mountainous areas, particularly in the coastal area of the Japan Sea.