It has been elaborated that reduction is one of the key processes for the mechanical reliability of an iron-based high-temperature water-gas shift catalyst. The process factors such as the heating rate, the reduction temperature, and the steam to gas ratio all have strong effects on the mechanical strength of the catalyst. For the catalyst pelletized in a laboratory, it has been observed that the mean value and the reliability of the mechanical strength can be increased much at suitable conditions, while under some conditions still often employed industrially these can be decreased much compared to the oxidized state. In the experiments, the best sample gains 37.3% and the worst loses 24.7% of the mean strength. In the same set of experiments with a narrow range of variation of the factors, the probability of strength failure of the best sample at 10 kg/pellet is 8 orders of magnitude lower than that of the worst. The analysis shows that the factors mentioned and the mean strength can be regressed by a second-order relationship. The temperature-programmed reduction and magnetic susceptibility measurements reveal that the ferromagnetic property of the reduced samples contributes a lot to the increase of the mean strength. The experiments with a commercial catalyst at several conditions also show a decisive effect of the factors on its mechanical reliability. It is plausible that the catalyst has different mechanical reliability in different positions in the industrial converters after reduction.