An external catalyst cooler is used to remove extra heat to ensure the heat balance in the system of fluid catalytic cracking (FCC). However, the single inlet in the cooler is difficult to make the catalysts distributed uniformly in the inlet region. Moreover, the catalysts streaming deviate from the original flow direction due to effect of valve plate. These influence their long period of stable operation. A pilot scale cold mode experimental device was built to study and optimize the catalysts distribution and deviation of flow direction in the inlet region of the external catalyst cooler. The effect of operation conditions on catalysts distribution and deviation of catalysts flow direction was measured. And two new inlet structures were designed to improve the non-uniform flow and deviation of catalysts flow direction. The experimental results showed that for the original inlet structure used in industry, the non-uniform distribution of the catalysts was first increased and then decreased with increasing the solid mass flux (Gs) in inlet tube. The worst circumferential distribution of catalysts occurred at Gs=230~620 kg/(m2?s) and ug=0.2~0.35 m/s. The deviation of catalysts flow direction was determined by locally asymmetric distribution index. The index increased and then decreased as the solid mass flux increased. The maximum value was presented at Gs=380~720 kg/(m2?s). After installing two new inlet structures, the catalysts mass distribution in the inlet region of the external catalyst cooler got more uniform and the deviation of catalysts flow direction was weakened. The inlet structure 2 had better optimization effect on mass distribution and symmetrical distribution of catalysts. Pressure drop in inlet tube with structure 2 increased by about 0.14 kPa compared to that of the original inlet structure.