The Cenozoic volcanics in Tengchong area are of calc-alkaline series and might be divided into four eruption stages (N2, Q1, Q3, and Q4), which make up two magmatic cycles composed of basalt→dacite (Nz→Q1) and basalt→andesite (Q-}Q4) respectively.Studies by means of Pearce ratio diagram show that fractional crystallization seems to be the major cause for variation in petrochemical composition. Basalts of the first cycle might have originated from partial melting of the upper mantle. The fractional crystallization of the (Pl＋Cpx土O1士Mt) assemblage was the main factor responsible for the formation of dacite and the assimilation of small amounts of crustal materials. This cycle shows features of bimodal igneous suite in a tensional tectonic environment. Basalts in the second cycle might have resulted from partial melting of the early subducted oceanic crust, with the fractional crystallization of the (Mt＋PI＋Cpx士Opx) assemblage being the main factor for the formation of andesite. This cycle has characteristics of island arc volcanics, being real post-collision arc volcanics.