Si nanoquantum dots have been formed by self-assembled growth on the both Si—O—Si and Si—OH bonds terminated SiO2 surfaces using the low-pressur e chemical vapor deposition (LPCVD) and surface thermal decomposition of pure SiH4 gas. We have experimentally studied the variation of Si dot density with Si—OH bonds density, deposition temperature and SiH4 pressure, and analyzed qu alitatively the formation mechanism of the Si nanoquantum dots based on LPCVD surface thermal dynamics principle. The results are very important for the control of the density and size of Si nanoquantum dots, and have potential applications in the new quantum devices.