The present paper deals with volcanic rocks of the Changning-Menglian belt (C1-P 2) and the south Lancangjiang belt (P1-T3) in "Sanjiang" region, Southwest China. Based On geological and petrological characteristics of these volcanic rocks, the authors studied their major elements, REE and trace element and, furthermore, determined their tectonomagmatic types. Volcanic rocks along the Changning-Menglian belt are basalts and ophiolite complex of oceanic ridge paraoceanic ridge type, which represent remnants of the Lancangjiang ocean. The South Lancangjiang volcanic belt is a composite volcanic arc resulting from eastward subducting and collision of the Lancangjiang ocean. The two volcanic belts, distributed in pairs, are products of the Lancangjiang oceanic suture zone.