The invention discloses a method for directly detecting 
ammonia in 
wastewater by non-contact gas 
membrane diffusion-
electric conductance. The method comprises the steps that a sample solution is sucked by a 
peristaltic pump A, a quantitative loop is filled with the sample solution, after a six-way valve is switched, a 
peristaltic pump B drives and sucks an alkaline solution to make the alkaline solution sufficiently mixed with the sample solution, 
ammonia in the sample solution is all transformed into 
ammonia gas, then the 
ammonia gas enters a sample solution cavity channel of a 
membrane diffusion unit, and a certain proportion of the 
ammonia gas is not in contact with a hydrophobic membrane, diffuses into a received solution cavity channel on the other side and turns into 
ammonium ions. Through a 'flow stop' or 'flowing' 
dialysis mode, a received solution which contains the 
ammonium ions enters the received solution cavity channel of the 
membrane diffusion unit and flows through a conductance 
cell, and an electrical 
conductivity detector directly measures the ammonia content according to the 
conductivity change of the solution. Compared with the prior art, the method has the advantages that the method has 
high selectivity, does not need 
distillation and color rendering, and is good in sample adaptability, wide in 
linearity range and long in service life of membranes, no toxic 
reagent is used, and the ammonia in 
sewage or recycled water can be directly determined within 5 minutes.