Objective: To study the soluble calcium ion content of different compatibility of Maxing Shigan tang and to discuss the compatibility regularity of Maxing Shigan tang. Method: The ICP-AES was used to study the soluble calcium ion content of each single herb about their different compatibility and different soaking and boiling time in Maxing Shigan tang. Result: All of herbs except the Almond in Maxing Shigan tang contained calcium. Gypsum had the highest content of calcium

followed by Ephedra

Licoroce had the lowest. The calcium ion content was decreased when Gypsum compatible with other herbs. Gypsum decoction had the highest content of calcium

followed by Gypsum Ephedra

Gypsum Licoroce and Gypsum Almond groups; Gypsum Ephedra Licoroce group had the lowest content of calcium. The calcium ion content of Maxing Shigan tang group was higher than that of Gypsum Ephedra Licoroce group. The calcium ion content of gypsum and Maxing Shigan tang group was increased with extend time of soak

but was increased first and then decreased by extending the boiling time. Especially

in the group of Gypsum and Maxing Shigan tang theoretical value

the calcium ion content declined rapidly. Conclusion: The calcium ion content can be decreased when Gypsum compatible with other herbs and increased by extending the soaking time. The calcium ion content was increased first and then decreased when extending the boiling time. The Gypsum compatible with Ephedra

Licoroce and Almond will not increase the calcium ion content

but can keep it in a stable range.