To determine potassium, there is a variety of instruments available for use, but they are quite different in working principles, performance, advantage and shortcoming. In this study, comparison was made between Inductively Coupled Plasma Spectrometer (ICP), Atomic Absorption Spectrometer (AAS), M410 Flame Photometer (FP-M410) and HG-5 Flame Photometer (FP-HG-5) in detection limit, linear range, stability and interference resistance of potassium determination. Results show that the detection limit was 0.16 mg L^-1 for ICP, 0.002 mg L^-1 for AAS, 0.005 mg L^-1 for FP-M410 and 0.007 mg L^-1 for FP-HG-5, and the maximum linear range 1 000, 3, 100 and 60 mg L^-1, respectively. Their acid interference resistance followed an order of FP-HG-5 > ICP > FP-M410 > AAS, while their salt interference resistance did an order of FP（HG-5）> FP（M410）> ICP > AAS, which was subject to some variation with the type and concentration of the salt. The comprehensive comparison reveals that ICP is suitable for determination of K relatively high in concentration and a variety of other elements simultaneously, but the cost of its operation for potassium measurement alone is relatively high; AAS is suitable for determination of K relatively low in concentration with a narrow linear range, but the addition of Sr and dilution of high K solution may reduce its efficiency, and moreover its operation cost is also quite high; FP-M410 is easy to operate and low in cost, but susceptible to interference and hence low in stability; and FP-HG-5, with Li internal standard is low in detection limit, good in stability, proper in linear range and high in resistance to the interference of acids or salts, which suggests that FP-HG-5 is the first choice for accurate determination of potassium.