Abstract: By means of X-ray diffraction, electron microprobe and mine-ralographic Lest the ingredient of Z-type mold coating used for making centrifugal cast steel pipe has been analysed. The results show that the coating consists of zircon (ZrSiO₄), bentonite, oxide ferric and a little high polymer. After sintering at high temperature high polymer decomposes or volatilizes, zircon and bentonite remain in a crystal state and the grains of bentonite refine. On the surface of the bentonite a thin layer of liquid film forms and then strenth of the coating decreases.