采用正交函数、导数光谱法分别测定复方土荆皮酊中苯甲醚、水杨酸、土荆皮含量。苯甲酸用正交函数法在220～230nm区间，△λ＝2nm，6个波长，支测定，计算P₂值，以含量对P₂值作线性回归，r＝0．9986；水杨酸在265～330nm区间作一阶导数光语，△λ＝1nm，在309nm处以含量对谷极值作线性回归，r＝0．9995；土荆皮在360nm处测定，其浓度正比于吸收值，作线性回归，r＝0．9982。3个组分回收率±RSD依次为99．25％±1．12％，99．39％±0．44％，99．25％±1．00％。

We proposed a method of determination for benzoic acid,salicylic acid and Pseu-dolaricis, in tincturae cortex Pseudolaricis Co.Benzoic acid was measured at 220～ 230nm ,at 2nmintervals,using 6-point quadratic orthogonal polynomial to calculate P_2. Linear regression was ob-tained for the content vs P_2 value,r=0. 9986. Salicylic acid was measured by l-order derivativespectrum,at 265～330nm. linear regession was obtaied for the content vs valley depth,r=0. 9995.The content of pseudolaricis was measured by the absorbance at 360nm.Its concentration was proportional to absorbance,with r=0.9982 for the linear regression.The mean recoveries(±RSD) of the three ingredients were 99.25%±1.22%,99.39%±0.44%,99.25%±1.00%,respectively.