Abstract: The yuanhua (Dephne genkwa Sieb. et Zucc.) root injection is a pharmaceutical preparation manufactured directly from yuanhua root crude drug. Its composition is complex. It is difficult to determine the content of the active principles. The chief absorptive components are diterpene orthoesters including yuanhuacine, yuanhuadine, yuanhuafine, yuanhuatine etc. and, of them, the highest content is yuanhuacine. So, the pure substance of yuanhuacine is used as a standard in this paper, and a novel method of orthogonal function spectr0photometry is developed to determine the content of total diterpene orthoesters (calculated on the basis of yuanhuacine) in yuanhua root injection. The mean recovery of yuanhuacine is 98.9% and the coefficient of variation is 1.6%. (n=9).