Abstract: A computational analytical method of simultaneous determination of components in compound drug without preliminary separation has been proposed. It is a matrix computation by means of multi-standard addition spectrophotometry on multi-wavelengths. The compound tablets of sulfamethoxazole was used to perform the experiment. In the experiment, the rule of error propagation for matrix computation was taken for the selection of solvent, groups of wavelengths and faction of standard addition, and the suitable concentration of standard addition was decided by test. In the case of determination for the simulated solution compound sulfamethoxazole, the recoveries for SMZ and TMP were 99.26～101.8 and 97.77～102.0%, respectively, with standard deviation of less than 0.51% and 213%, respectively. The method had been applied to the determination for compound tablets of sulfamethoxazole with satisfactory results.