The erosion resistance performances of high-Cr cast iron Cr15Mo3 and three kinds of structural ceramics, a-Al2O3, ZTA, Si3N4, were investigated in flowing suspensions of solid particles with a rotary disk erosion wear tester. The microcosmic failure mechanisms of their wear surfaces were analyzed. The results showed that the erosion resistance of Si3N4, ZTA, a-Al2O3 is 21.8, 8.2, 5.6 times than that of Cr15Mo3 respectively. For ceramic materials, toughness and strength are two main factors that affect erosion resistance rather than hardness. The wear rate of ceramic materials is in proportion to the strength and the biquadratic toughness. Due to erosion, Cr15Mo3 is worn out most in the whole, the erosion holes are very clear and its failure pattern is in “W” shape. The wear of ZTA and Al2O3 mainly occurs in the binding phase of the crystal boundary. Thus, the crystal grains are exposed, but without breaks and cracks. The failure pattern is in the shape of “U”. Si3N4 only loses some binding phase of the crystal boundary and the erosion surface is smooth.