Abstract: Volcano is one of exiting modalities of substances redistribution in the earth. The origin of volcano results from that the state of the mantle solid substance is changed, resulting in substances' differentiation. When it happens, displacement reaction of substances appears on top of the mantle. And then the load of displacement space will decrease, causing the buoyancy increasing. In the end, volcanic eruptions will happen. There are basic conditions for the formation of volcanoes, namely, displacement substances, displacement space and eruption channels. There are five existing states of volcanoes: perennial, intermittent, opening, ending and under-erupted ones, which are highly related with the velocity of substance displacement. And it keeps a close relationship with the velocity of solid substances' state change. Volcanic eruption results from substances emission in the earth, which can also cause volumetric change of the earth, namely crust movement. Intensity of volcanic eruption is in proportion to the thickness of the crust. If the crust is thinner, volcanic eruption can not happen but only overflow. And if the crust is thicker, greater pressure will produce in the displacement space. Pressure inside of the volcano is closely related with displacement height and density of the substance, by which the pressure can be calculated. Distributions of volcanoes are also interrelated to the distribution of solid substances of the mantle. And the distribution of the volcanoes in geohistory periods is strongly affected by the degree of impinging planetesimals, and that in later periods is mainly affected by subducted plates.

Key words: volcanic origin, pressure, state, process