On the basis of the study of different temperature and catalyst, the effect of hydrogen and nitrogen on the morphology and yield of boron carbonitride(BCN) nanotubes produced by thermal decomposition at 860℃ was studied. It is found that nitrogen has a little effect on the growth of BCN nanotubes. Different from nitrogen, transmission electron microscopy(TEM) images reveal that hydrogen is important to the growth of BCN nanotube. Bamboo-shaped thinner wall nanotubes with higher yield are produced with hydrogen flow rate of 40 sccm, whereas curved nanotubes with lower yield and are generated with hydrogen flow rate of 0 sccm. BCN nanotubes with some holes on were produced with the flow rate of 80 sccm. Basic on previous analysis, we think that the appropriate range of N2 should be 150—210 sccm, and that of H2 should be about 40 sccm. At last, the reasons were also analysised.