To solve the problems that the traditional ammonia detection methods were complex, not easy to maintenance and difficult to realize quick measurement in situ, an intelligent ammonia sensor has been designed in this paper. The intelligent ammonia sensor integrates ammonia electrode, pH electrode and Ammonium ion electrode together to realize the In situ detection of ammonia. Because the output signal of ammonia electrode is weak and easy to be disturbed by external interference, a low-pass filter circuit has been designed, this kind of circuit have a good effect. The test results have shown that the sensor is easy operation, low cost and no pollution.