Abstract: BiPLS combined with IR was used for the rapid determination of dynamic viscosity in used lubricating oil.In order to improve the measurement accuracy of the viscosity calibration model,backward interval partial least squares (BiPLS) algorithm were applied to the efficient extraction of spectral information on viscosity changes.The spectrum with wavenumber from 4 000 cm-1 to 400 cm-1 was divided into 12 intervals.With the 4 subintervals of 2,10,11,12,the corresponding wavenumber ranges of 1 300-400 cm-1 and 3 700-3 400 cm-1 were selected.The standard error of calibration model found was 0.031 5.According to the verification result of the predicted accuracy of model,the method had good correlation with the standard method for dynamic viscosity.The model could be used for quantitative analysis of values of dynamic viscosity of used lubricating oil at 40 ℃.