Abstract: Abstract: The pH value is an essential physical and chemical parameter in crop growth. The monitoring of pH value is vital for the regulation of crop growth environment and the increase of agricultural production and income. Considering the problems of fragile front-end probe and slow charge transfer caused by large internal impedance in the current traditional commercial pH sensor, a flexible sensor chip based on polyaniline sensing mediated by Single-Walled Carbon Nanotubes was prepared by using inkjet printing technology. The flexible chip comprises a sandwich-type membrane structure, including a polyimide substrate, a nano silver wire layer, a single wall carbon nanotube dielectric layer, and a proton acid doped polyaniline ion-selective membrane. The differences in impedance and charge transfer between flexible pH sensor chip and commercial pH sensor were analyzed by scanning EIS impedance at the electrochemical workstation and analyzing fitting circuit parameters. Compared with the commercial pH sensor on the sensitivity, response time, stability, repeatability, and anti-interference. The 0°~120° bending influences were analyzed. The feasibility was verified through the dynamic pH monitoring in the soilless cultivation. The experimental results show that: firstly, the charge transfer impedance of the flexible pH sensor chip was 230.8 Ω. Moreover, the value of the commercial pH sensor was 9 879 Ω. The charge transfer impedance of the flexible pH sensor chip was 1/4 of that of the commercial sensor, which confirms the advantages of the flexible pH sensor chip in the advantages of a lower impedance and a faster response. Secondly, the pH detection range of the flexible pH sensor chip was 2~10. The sensitivity was –60.1 mV/pH. The pH detection limit of the commercial pH sensor was 1.68~12.46. The sensitivity was –55.2 mV/pH. The performance of the flexible and commercial pH sensors was similar. The response time of the flexible chip was about 15 s, which was significantly lower than that of the commercial pH sensor, 34 s. In the stability test, the maximum drift of the flexible pH sensor was about 5.44 mV within 12 hours, and the maximum drift of the commercial pH sensor was about 3.4 mV. The pH deviation of the repeatability test of the two sensors was smaller than 0.05. It demonstrated good anti-interference to Na+, K+, Ca2+, Mg2+, and Cl-. The flexible pH chip quickly responded when dripping NaOH or HCl solution. When the flexible pH sensor was bent at 0°~120°, the sensitivity illustrated neglectable changes, and the corresponding maximum deviation was only 15.8 mV. The bending did not affect the accuracy of the flexible pH sensor chip. The maximum absolute error of the flexible pH sensor chip for calibration curve verification was 0.24, the maximum relative error was 6.7%, and the corresponding pH verification value was 3.80. The maximum absolute error of the commercial pH sensor was 0.1, and the corresponding pH verification value was 5.9. The maximum relative error was 2.2%, and the corresponding pH verification value was 3.64. The relative errors of the flexible pH sensor chip and the commercial pH sensor were within 6.7% and 2.2%, respectively. The temperature drift of the flexible sensor chip is less than 0.23, and its service life is more than 14 days. Finally, the flexibility showed good consistency with the commercial pH sensor in the dynamic monitoring of the pH in Hydroponic Lettuce cultivation. The variation range of pH values monitored by the flexible pH sensor chip was from 5.4 to 6.3. Furthermore, the maximum pH monitoring deviation between the flexible pH sensor chip and the commercial pH sensor was 0.12. The flexible pH sensor chip was proven with good consistency and accuracy with the commercial pH sensor, which can quickly and accurately obtain the pH change of the measured nutrient solution.