Abstract: Two kinds of doped YAG crystals of thirteen groups being grown by Czochralski method have been analyzed. It has been proved that the compo-sition of the doped crystals is definitely rich-in rare earths and is indepen-dent of the composition of the melting matrix, the condition of crystalgrowth and the atmosphere of the furnace.In this paper we have firstly determined the formula of YAG crystal and the variance in its composition.