Abstract: This paper briefly introduces the basic knowledge, principle and method of the application of Kalmanfiltering spectrophotometry in multicompound analysis. In the example of Annaka injection, the proposed method determined the contents of sodium benzoate and caffeine simultaneously, while considering the system error and the linear drift problem. For comparision, the experiment data were also treated by least square method and their accuracy and precision were comparable. The proposed method provides a simpler and quicker way than the pharmacopoeial method.