Abstract: The range-energy relation of a proton when impacting on the N-4 nuclear emulsion plane were investigated using classical SRIM Monte Carlo program and curve fitting method, covering the incident proton energy range from 0.001 to 14 MeV and the incident angle range of 0°~30°. A definite analytic expression was derived from this simulation with the errors below 1%. The results have extraordinary significance for the preparing and prediction of some experiments.