A detector of crop leaf EC based on the Four-Electrode method was developed.High correlation was obtained between the electrical property and water content.The correlation coefficients had a downward trend as the growth period advanced.The relative water content (RWC) and leaf EC had the best correlation. Water is indispensable to plants and the shortage of such critical resource leads to a decline in land productivity and yield loss. Leaf water content is an important factor to show water scarcity in farmland. Since the physiological electrical property of plants was found to have relation with leaf water content, a detector of plant electrical property based on the Four-Electrode method was thus developed. It consisted of four probes, two current probes injecting constant alternating current into the object and two voltage probes measuring the voltage drop between two electrodes. The voltage drop was then used to reflect the electrical property and evaluate the water content of plant leaves. Corn was selected as the research object, and the experiments were conducted. Corn leaves were tested at different growth stages and water status, and the electrical property of corn leaves was measured. Three indexes were calculated as the indicators of corn leaf water content, dry base water content (DWC), wet base water content (WWC), and relative water content (RWC). The leaf electrical property was observed to have a negative correlation with all three parameters of water content. Correlation coefficient had a downward trend as the growth period advanced and the highest correlation coefficient was obtained in the seedling stage. In each test, the relative water content (RWC) had the best correlation with the leaf electrical property. It is shown that the electrical property of corn leaves can be used to effectively evaluate the water stress.