The MOCVD(Metal-Organic Chemistry Vapour Deposition) technology has already been important means in research and production of semiconductor membrane material at these years. The metal-organic compounds are often used to be the raw materials of MOCVD in electrical material industry. Trimethyl gallium is one of the key raw materials. By chemical characteristic, trimethyl gallium is much reactive. It is easy to explode if touches water or air. Hence, we study the safe and correct decomposition of trimethyl gallium,and also study the analytical method of determining high purity trimethyl gallium. In this paper, we developed a method of determining Al,As,Au, B, Ba, Be, Bi, Ca, Cd, Co, Cr, Cu,Fe, Ge, Hf,Hg, Mg, Mn, Mo, Nb,Ni,Pb,Sb,Sc, Si,Sn, Sr, Ta, Ti,V, Zn, Zr etc. 32 trace impurity elements in high purity Ga(CH3)3 by ICP-AES.