For hydrogen isotope enrichment/separation applicable to fusion fuel processing, environmental tritium safety confinement, or recovery of tritium from heavy water reactors, a hydrogen displacement adsorption process system is recommended using molecular sieve 5A as the separation material. For simulation and optimization of the process, mathematical models and a solving method are provided to calculate the breakthrough curves during the displacement adsorption, in which various parameters including pressure drop and mass transfer coefficients are allowed to be changeable. Based on the calculated results, the effects of the column size, the flow rate, and the outlet pressure on the enrichment factor, the recovery ratio and the separation ability of the column are comprehensively analyzed. The conclusions have some theoretical guiding significance for the development of hydrogen isotope separation by the displacement adsorption method.