The invention relates to a kit for diagnosing / measuring kalium (ions) by utilizing the technologies of the enzymic colorimetry and the enzyme linked immunosorbent assay. The invention further relates to a method, a principle and the composition and the components of a reagent for measuring the concentration of kalium (ions), and belongs to the technical field of medical / food / environmental inspection and measurement. The main components of the kit include a buffer solution, coenzyme, adenosine diphosphate, enolphosphopyruvate, coenzyme A, pyruvate kinase, pyruvate oxidase, NAD(P)H oxidase and a stabilizer. Through mixing a sample and the reagent by a certain volume ratio, a series of enzymatic reactions occur, then the reactant is placed under an ultraviolet / visible light analyzer, and the velocity of the increase in absorbance at 340 nm of the dominant wavelength is detected, thereby measuring the concentration of kalium (ions).