Couplet medicines,also known as “couplets”,“pairs”,“brothers” and “sister” medicines, are commonly used in clinic,relatively fixed compatibility of two medicines,is the smallest unit in the compatibility of traditional Chinese medicine,but also the basis of complex prescription composition . Professor Wang Yongjun,proceeding from the classical theory of kidney essence, inherited the characteristics of Shi's theory of traumatology,took filling kidney essence as the fundamental method,used the pairs of Fructus Cnidii and Fructus Ligustri Lucidi to treat osteoporosis. This paper summarizes Professor Wang Yongjun's experience in clinical and scientific research,analyzes the compatibility principle of the couplet medicines, and explores its pharmacological mechanism for osteoporosis.