The invention discloses a measuring method of asymmetric dimethylarginine concentration, comprising the steps of: subjecting a sample to be measured to a reaction in an enzymatic cycling reaction system, measuring and calculating the generation rate of ammonia from the enzymatic cycling reaction, thus obtaining the content of asymmetric dimethylarginine in the sample to be measured. The enzymatic cycling reaction system consists of dimethylarginine dimethylaminohydrolase, citrullinase, ornithine carbamoyltransferase, and carbamyl phosphate or its salt. The invention also discloses a measuring reagent corresponding to the method. In the invention, an enzymology measuring method and a measuring reagent of asymmetric dimethylarginine are established for the first time. Needing no special instrument, the method of the invention has simple operation, high sensitivity and low cost, thus being able to realize rapid and high flow sample detection in clinic. Thus, asymmetric dimethylarginine is probable to become a conventional inspection item in clinic. Therefore, the method provided in the invention is of great scientific and economic value.