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Compared with conventional laboratory chemical analysis, ion selective electrode (ISE) is time-saving, low-cost, ease of use and pollution-free. To detect soil nitrate nitrogen content rapidly, a nitrate ion selective electrode could be used. This paper studied characteristics of nitrate ISE. Potentiometric experiments utilizing nitrate ISE to measure sodium nitrate solution were conducted during the study. A linear regression model based on the Nernst equation was built using the least square method. Several groups of potential values were measured at one concentration and then the arithmetic mean of them was calculated. These mean values and their corresponding concentrations were used in LSM to reduce the impact of the relatively poor repeatability of ISE and reduce nitrate concentration prediction errors. The feasibility of the modeling method was verified using prediction errors as an index. In this study, extra data points except the calibration points were used to test the prediction error. Except several singular points, the relative error of this model was from 1.3% to 13.67% (absolute value). Compared with calibration each time, this modeling method can be used to determinate the nitrate concentration if ISE will be calibrated after using for a certain number of times.