Abstract: The dielectric constant and relaxation spectrum of palm oil fried 2 ～ 10h (two hours interval) at 150, 180, 210℃ were measured by dielectric constant and low-field NMR.The comparison between the dielectric constant (ε) and the free fatty acids determining by GC was made, and the correlations between the ratio of relaxation peak area (S21/S22) and the ratio of oleic acid and palmitic acid (O/P) was made either.The results showed that:the degree of deterioration of palm oil could be monitored by the dielectric constant (ε) at 150, 180, 210℃ accurately.Relaxation time T21, T22 could be used to distinguish whether the palm oil was processed at high-temperature frying.At 150, 180℃, the trend between S21/S22 and O/P was similar, the correlation of which was positive and significant (p<0.05, p<0.01) .So the S21/S22 could be used to analyze the quality of frying palm oil.At 210℃, there was no correlation and similar trend between S21/S22 and O/P.