The prescription is composed by drugs. Through the order compatibility， the drugs can enhance their function， and play a complementary role， and it can make the various characteristics of the drugs combined into an entirety. The core of compatibility of drugs is particularly critical， because it determines the main function of the whole prescription and the attending orientation. This paper from the core function of traditional Chinese prescription compatibility theory， Chinese medicine literature， modern pharmacological research， TCM clinical application provides proofs to certify Radix Rehmanniae Praeparata， Fructus Corni， Rhizoma Dioscoreae as the core function of Liuwei Dihuang wan.