Abstract: Utilizing the peculiarities of strong penetrating ability of NIR diffuse reflectance,conveniency and rapidity of operation,digital grating-NIR diffuse reflectometry was applied to the determination of total phosphorus (expressed as P2O5) in the compound fertilizer,nitrophoska,including testings of standardization,establishment of mathematical model,verification and application.As shown by the experimental results,(1) only few minutes were required for a determination without the necessity of weighing of sample and the consumption of chemical reagents;(2) as compared with the quinoline molybdophosphate gravimetric method,value of standard deviation found in calibration was 0.13%,with correlation coefficient of 0.995 9;value of standard deviation obtained in verification was 0.15% with correlation coefficient of 0.994 8;(3) in the tentative application of the proposed method to the predictive determination of total phosphours in 52 samples of nitrophoska,the predictive standard deviation found was 0.29% with correlation coefficient of 0.985 0,which were very close to the values obtained in calibration and in verification.