Abstract: The effects of N, P, K nutrients and their proportion on relative protective enzymes in burley tobacco and the dynamics of relative substances were studied in field stage. The results showed that the peroxidase (POD) activ-ity and proline (Pro) content went up in early growing stage and went down in late growing stage, the peak stage was at 65d or so after transplanting. The polyphenol oxidase (PPO) activity and contents of total phenol, flavonoid were increased as the advance of growing and developing, characterized by a curve with single peak, and the peak was at 75d after transplanting. The malondialdehyde (MDA) content went up and total free amino acid content went down as the process of growth. The application rate of N, P and K was positively correlated with endogenous protective enzyme activity and the contents of relative substances. The N showed an extremely significant correlation with total phenol and significant correlations with POD, Pro, PPO and amylase. The effects of the three elements on the activity of protective enzymes and contents of relative substances were different, the effects on PPO, Pro, total free amino acid and amylase were N > P > K, on the contents of MDA and flavonoid were K > N > P, and on POD and total phenol were N > K > P.