We studied the black deposit(BD) in GaCl tube which caused depletion of reactant source and reduced the crystal quality on GaN growth by MHVPE(Modified Hidride Vapour Phase Epitaxy). It was observed the black deposit at a GaCl outlet temperature up to 550 ℃ and it was confirmed that the temperature range of 550~650 ℃ was the best condition of formation of the black deposit. We confirmed from SEM that the black deposit was showed the very thin and long tube shape, and head parts of tube's end were showed the spherical shape. We maked sure that the generated black deposits were composed of both gallium and carbon from EPMA, TEM and Micro-Raman.