The Rapid Mass Movement Simulation (RAMMS), requires input data such as DEM, the Voellmy-fluid friction coefficients, flow direction, and release information. To evaluate the uncertainties in RAMMS outputs using various input data, a real debris flow event was considered. After the calibration of the model, different scenarios were defined, which included different DEM cell sizes (1, 2, 3, 4, 5, 10, 15, and 20 m), different values of friction coefficients (the Dry-Coulomb type mu= [0.1, 0.2, 0.3]; the viscous-turbulent \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\:\xi\:$$\end{document}= [100, 200, 400, 800]), different directions of inflow (changes up to +/- 50 degrees with a 10-degree interval), and active or inactive consideration of terrain curvature. The final results showed: (a) by increasing the DEM cell size, holding all other parameters constant, the accuracy of the model outputs (e.g. overall inundation area) reduced intensively which was up to 724% for DEM-20 m in comparison to DEM-1 m; (b) the impact of the friction coefficient (mu) was much greater than the friction coefficient (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\:\xi\:$$\end{document}) on the results; (c) the effect of the terrain curvature activation on the results was not significant; (d) changing in inflow direction to up to +/- 50 degrees did not cause a significant change in the overall results.