Abstract: This paper describe the research on the mutual interference of Li, Rb, Cs in air-acetylene flame.It was concluded that the flame photometry gave the same results as the atomic absorption spectrophotometry for determming Li, Rb and Cs.Because of the low melting point of alkali metal elements, the lower stability in use and the shorter service life of hollow cathode lamp for alkali metal elements, the flame photometry still is widely used for the determining these elements of Li, Rb and Cs etc.