In view of the existing problems in the detection of agricultural conductivity, such as complex detection methods, large instrument volume and high requirements for internal components, and in order to improve the detection efficiency and reduce the size of the sensor, a single-walled carbon nanotube flexible conductivity sensor chip based on ink-jet printing was designed and fabricated. The sensor chip was modeled and calibrated by AC impedance spectroscopy. The response time, stability, repeatability, bending and packaging effect of the sensor chip were systematically tested, and the error between the flexible sensor chip and the commercial EC electrode was determined. The feasibility of applying the flexible chip to the on-line monitoring of EC of soilless lettuce nutrient solution was verified. The experimental results showed that the total chip area was about 30mm×40mm, realizing miniaturization of detection. The conductivity range of modeling and calibration was 25.8~3098μS/cm, and the measurement impedance range was 160~15000Ω. There was an obvious power function relationship between the standard conductivity value and the measured impedance value, and the correlation coefficient was 0.99. The absolute error range of the verification test was -99.76~115.62μS/cm, and the relative error range was -5.89%~8.02% (FS). The measurement results of the flexible chip were in good agreement with the EC standard value. The maximum response time of the flexible EC sensor chip was 10s. The stability fluctuation within 12h was 3.91μS/(cm〖DK〗·h), and the absolute error range of five repeated measurements was -74~62μS/cm. The stability and repeatability were in good agreement with commercial EC electrodes. Bending in the range of 0°~90° and PDMS packaging had no effect on its performance. In the monitoring of EC value of hydroponic lettuce for 10 consecutive days, the maximum deviation between the flexible EC sensor chip and the commercial EC sensor was 46μS/cm.The flexible chip showed good consistency with the commercial electrode, and its micro flexibility was more suitable for hydroponic rhizosphere monitoring. The flexible EC sensor chip can monitor the EC value of soilless culture nutrient solution in real time and accurately, which had a good prospect of agricultural application.