Abstract: By simulation experiments, a set of pottery-moulds were fired, in which distinctive content of plant ash was added to the raw materials. Then the chemical components of pottery-moulds were analyzed to find chemical characters of plant ash added. And the values of Ca/Al, K/Al, Mg/Al, P/Al, Mn/Al were used as chemical characteristic index for the discrimination of plant ash in row materials. Analytical results of components in simulated pottery-moulds showed that when the quantity of plant ash increased, the values of Ca/Al, K/Al, Mg/Al, P/Al, Mn/Al increased. However, the most of the ancient pottery-firing processes don′t have the plant ash as raw material and the chemical components could be considered as the clay of the raw material of ancient potteries. Statistical data for the analysis of the ancient potteries and ancient pottery-moulds showed that the plant ash content in the raw materials of ancient pottery-moulds was higher than that in ancient potteries. The comparison of values of Ca/Al, K/Al, Mg/Al, P/Al, Mn/Al between ancient potteries across China and pottery-moulds from different periods and provenances implied that plant ash may be an important constituent of ancient pottery-moulds.