Abstract: Comparative experiments were carried out on two kinds of nessler colorimetric method for soil ammonium nitrogen measuring, one was a conventional nessler colorimetric method (routine method), another was an improved method of nessler (speed measuring method). The test showed that the speed measuring method with wide linear ranged for 0-168 mg/kg; the whole process of testing time was 25 min, which was half of routine method; the speed measuring method had a sensitive and stability color, it could be stable for a few hours; the test results could show soil nutrient content directly; the speed measuring method could also be operated convenient, it had no need to be operated by operation staff with finished product reagent. In addition, the speed measuring method had the advantage of cost saving. Portable measuring instrument and matched detection method could meet the basic measuring requirement for soil fertilizer use.