The percent ammonia nitrogen was determined in Passaic River waste water using Ion-Selective Electrode EPA Method 350.3. The intelligent ammonia sensor integrates ammonia electrode, pH electrode and Ammonia Ion electrode together to realize the in situ detection of ammonia. The test results have shown that the sensor is easy operation, low cost and no pollution. The ammonia is determined potentiometrically using an ammonia ion selective electrode and a pH/mV meter, having an expanded millivolt scale. The ammonia selective electrode uses a hydrophobic gas-permeable membrane to separate the sample solution from an electrode internal solution of ammonium chloride. Dissolved ammonia is converted to NH3 gas by raising the pH to above 11.0 with a strong base. NH3 gas diffuses the membrane and changes the internal solution pH that is sensed by the electrode. In single laboratory test results have been found 1.001 NH3-/L and 0.897 mg NH3-N/L, recoveries were 77.3% and 83.1%, respectively.