In order to develop a method for rapid detection of total potassium content in leaf of maize, electrical impedance measuring method was used to collect the electrical impedance parameter of the leaf tissue juice under different potassium levels, and the relationship between impedance value and total potassium content of the leaf were investigated. Using stepwise regression method to choose the sensitive frequency for the total potassium content, every regression model included two sensitive frequencies based on which the linear regression equation was the best with the correlation coefficient of 0.83 at least and root mean squared error of 0.16 at most for four growth periods respectively. Therefore, it was demonstrated that impedance value could be a predictor for maize leaf potassium content. Electrical impedance measuring technology could be an available method for potassium fertilizer recommendation in crop.