A three-flow-tube, quasi-one dimentional calculation was carried out to estimate modetransition fuel equivalence ratios under clean and vitiated inflow conditions. A simple flame holding model was used in the calculation. In cases of vitiated inflows, both total temperature and total enthalpy matched conditions to that of clean air were tested. Calculated wall pressure distributions were well matched to those of experimental values, qualitatively. Additionally, the ratio of mode-transition equivalence ratio of clean inflow divided by that of vitiated inflow was well matched to that of experimental value. Matched total enthalpy was effective to eliminate the inflow vitiation effects on mode-transition equivalence ratios in a case that thermal choking was attained at constant area exit. However, in a case that thermal choking was attained in the diverging region, matched total enthalpy was not effective.