Abstract: A model and a simulation method for calculating the proton Single Event Upset (SEU) cross section are presented by analysis of proton reactions in silicon.The variety,production cross section,energy spectrum and double differential cross section are calculated for the secondary particles produced by reactions of high energy protons in silicon.The reaction in silicon is simulated with Monte Carlo method.The range of secondary particles is computed with TRIM code.The energy and charges deposited by secondary particles are calculated in sensitive volume in memory cell.Whether a proton induced SEU is determined by comparing the charges with the critical charge and the proton SEU cross section is obtained.The calculation results are in agreement with the experimental results.