The invention relates to preserved rehmanniae and a preparation method thereof.The preserved rehmanniae takes rehmanniae as material and is made by adding with compound material. The preserved rehmanniae contains 50-100 shares of fresh rehmanniae, 40-70 shares of 
sucrose, 2-5 shares of salt, 0.1-0.2 shares of 
citric acid, and 0.08-0.15 shares of 
alum. The manufacturing method of the invention includes the process: the material is selected, washed, with peel removed, 
cut, dipped in 
salt solution, rinsed in 
clean water and desalted; the material is heated in boiling water containing 
alum, taken out, cooled in cold water, and then drained; 
sugar and the 
citric acid are added for preservation; the material is added with 
sugar and is boiled for twice; then the rehmanniae blocks are taken out, with 
sugar solution dropped, and are dried and packed, thus obtaining the invention. The manufacture process is reliable and the preserved rehmanniae can be produced by using the current production condition of the preserved fruit.The preserved rehmanniae made by the invention is sweet and delicious in taste without foreign 
flavor. Besides, the preserved rehmanniae keeps rich 
mannitol, rehmannin, 
vitamin A and a plurality of amino acids in rehmanniae. The invention has the function of nourishing essential fluid, reinforcing 
kidney, improving the five viscera, invigorating vital energy and energy, etc.After long-term drinking, the invention can prolong life, prevent hairs from graying, and improve health.