Abstract: By determination of toldrin in the presence of the interference of lactose, the effect of general or non-special operation error on the methods compared or estimated was investigated and discussed. The approach for checking and measuring the operation error was proposed, and the advantage of the linear ombination method of absorbances (LCM or LCMA) was further confirmed. Meanwhile, the relation between accuracy and the number of points combined, and the effect of the low absorbance value of the main component on the accuracy of LCM were discussed. The importance of the ratio between correspondingabsorbances of two components in LCM was investigated.