Computer simulations were performed to study the temperature and velocity distributions and the interface shapes in the floating-zone melt for lithium niobate materials. The input power distribution generated by the heat source was assumed to be Gaussian. The variation of the interface shapes and the transport phenomena in the flow zone relative to the input power was investigated. The results show that the shapes of the gas-melt and melt-solid interfaces and the temperature and velocity fields are modified by the gravity force; the influence of gravity increases as the input power increases. The present results are consistent with the recent experimental observations.