Abstract: The level of ammonia nitrogen source is one indicator of eutrophication of lakes and reservoirs. Currently, indigo phenol blue spectrophotometry and Nash reagent spectrophotometry have been adopted to detect the NH₃-N content in national standard of the People's Republic of China. To cultivate college students' innovative practice, scientific research consciousness and experimental hands-on ability, the ammonia nitrogen concentration in the water samples of three famous springs (Baotu Spring, Heihu spring, Wulong pool), Daming Lake, Dongchang Lake and Haihe river was tested. Taking the drinking water from Shandong Normal University for comparison, the differences between the two methods were studied. More importantly, the students learned from the success and failure in the testing process that they used the colorimetric method to detect and analyze samples. The correlation coefficients of the standard curves of the two methods reached up to 0.9999 through continuous improvement of the detection scheme. In the experimental operation, different experimental results have been obtained due to the variation of operation and manipulation (such as the concentration of chromogenic agent, the operation skill of the standard solution and the length of the time after the mixing of each solvent etc.). This paper analyzes the causes of the outlier in the experimental results, and discusses the difference of two detection methods.