The invention relates to the technical field of preparation of medicinal plant extracts, particularly to a preparation technology of a high-purity medicinal plant extract with membrane capacitance electro-adsorption process, and overcomes the problems of low salt ion removal rate, low effective component recovery rate, long concentration treatment time and easy bacteria breeding in the existing ion exchange method or nanofiltration method treatment process. The technology includes: (1) a rough preparation process: filtering a medicinal plant by crushing soaking method or decoction method to obtain a first-stage mixed solution; (2) a purification process: introducing the first-stage mixed solution into a membrane capacitance electro-adsorption device for preferential adsorption of heavy metals with bivalent charge ions or above, also adsorbing other monovalent ions in the continuous adsorption process, and subjecting the first-stage mixed solution to device adsorption treatment at leastonce so as to obtain a second-stage mixed solution; (3) a dehydration process: introducing the second-stage mixed solution into a reverse osmosis device to remove excessive moisture of the mixed solution, and letting a third-stage mixed solution flow out of a concentrated water outlet; and (4) a drying process: drying the third-stage mixed solution at a low temperature to obtain the high-purity medicinal plant extract.