Abstract: According to the field trials with quantitative fertilization, the spectral characteristic parameters which were highly significantly correlated with foliar potassium (K) content were screened out using Pearson correlation analysis, and the foliar K content estimation models of Juglans regia ‘Wen185’ in different phenological periods of fruit development were built up with these parameters as independent variables using regression analysis. The results showed that there were one or more spectral characteristic parameters which were highly significantly correlated with the foliar K contents of ‘Wen185’ walnut in the different phonological periods of fruit development (P＜0.01). Through cubic function analysis with normalized difference green index in the fruit setting period, ratio red and yellow edge area index in the fruit rapid-growth period, ratio green index in the fruit fat-change period and blue edge area in the fruit near-mature period as independent variable, the regression estimation models of the foliar K content in the different phenological periods of fruit development were established respectively, and their fitting degrees (R²) were all above 0.95. In addition, the estimated values of the models for the foliar K content of ‘Wen185’ walnut were consis-tent with the measured values of the independent samples, and the root mean square errors and the relative errors of the independent sample tests were less than 0.8161 g·kg^-1 and 2.7% in the diffe-rent phenological periods of fruit development. The models showed their high estimation accuracy. The spectrum technology possessed great application potential in monitoring K status of J. regia.