Abstract: The effects of water-soaking on properties of the fused-iron catalyst for ammonia synthesis were investigated.The results show that both the mechanical strength and catalytic activity of catalyst All0－5Q decline after water-soaking,while its specific surface area and the pore volume increase.Both the water-soluble potassium and water-insoluble potassium exist in the fused-iron catalyst,and usually the amount of the former is far more than that of the latter.Two kinds of potassium ferrites, KFeO_2 and K_1＋_xFe_(ll)O_(17)（x＝ 0～1） were prepared and their leaching processes were investigated respectively.KFeO_2 can be readily hydrolyzed.In contrast to KFeO_2,potassium can not be resdily dissolved out from K_(1+x)Fe_(11)O_(17) by Water.It is suggested that KFeO_2 with KOH,KAIO_2,K_2CO_3,etc belongs to the water-soluble potassium,which occurs mainly on the bounderies of the crystal grains of Fe_3O_4,While K_(1＋x)Fe_(ll)O_(l7)belongs to the water-insoluble potassium,which is uniformly distributed in the grains of Fe_3O_4.Both watersoluble potassium and water-insoluble potassium in the fused-iron catalyst promote the catalytic activity of ammonia synthesis,but the contribution of the former is less than that of the latter.