Abstract: According to the field geological characteristics and petrology of the Taima rock body(now known as Taima rockdome) which is the main body of Shiwandashan rock belt, the authors consider that the Taima rock body consist of porphyroclastic lavas and is an eruptive facies but not an intrusive phases of granite porphyries. Combined with the surrounding volcanic rocks, intrusive rocks and strata, the Taima rock body is considered as a dome of the central part of the central fissure type volcanic structure. Therefore, the Shiwandashan rock belt is a volcanic-intrusive complex rocks belt, and the Taima porphyroclasts lava is one of the phases in that belt.