Two-dimensional transition metal dichalcogenides show a potential application in photoelectronic devices due to their excellent electronic and optical properties. These excellent properties benefit from large single crystals. Here, we demonstrate that large single crystal monolayer MoS2 can be synthesized on rough SiO2/Si substrate via chemical vapor deposition (CVD) method. Rough SiO2/Si substrate has two advantages. The first one is low nucleation density. The rough substrate with "hill and valley" structures can effectively suppress nucleation density. The lower nucleation density seems to be caused by the reduced surface concentrations of reactants, which has been verified by solving the diffusion equation. Another important advantage is the higher growth rate. We found that the free-standing MoS2 films were successfully grown over the "valley" regions of the rough surface. The calculated growth rate of free-standing MoS2 is three times as that on polished surface, which comes from the introduction of temperature gradient during suspended growth. Our findings have provided new insights into the mechanisms underlying CVD MoS2 growth on rough surfaces and are expected to accelerate the development of directly suspended growth of two-dimensional material for further device applications.