Abstract: To study the contents variation of main components in Fructus Corni (FC) after combination with Radix Rehmanniae Prepatrata (RRP). The reciprocity of FC with RRP were investigated by means of high performance liquid chromatography (HPLC) and electrospray ionization mass spectrometry (ESI-MS) technique in the negative ion mode. FC with RRP was decocted separately, and then the separate aqueous extracts were combined partly. Different proportions of FC with RRP were decocted together. The contents of Morroniside, Loganin and Gallic acid in these samples were analyzed, synchronously, mass action of these samples were examined. FC with RRP promoted each other in dissolving percents in certain suitable quality proportion (FC∶RRP ≤ 4∶8). Together decocted and single-decocted merger can produce different new materials. The existence of RRP has great influence on the dissolution of components in FC which would not restricted by temperature. It provides a certain science basis for the reasonable Chinese herbal medicine.