This paper presents a research on the problem of catalyst failure in a selective catalytic reduction (SCR) system. The preliminary analysis indicates that the catalyst failure is caused by abrasion. For this, firstly, the mechanism of abrasion is analyzed through a field experiment. Secondly, according to the results from the field experiment, a scheme is put forward to optimize the flow field. Finally, the application results show that the uniformity of fly ash distribution in the flue gas are improved prominently, the reliability of the SCR system is enhanced at the same time.