The structure and dynamic viscosity of molten metal In in the temperature range from 280 to 750℃ and investigated by using a high-temperature X-ray diffractometer and a torsional oscillation viscometer. The experiments show that the nearest interatomic distance r1 and the corrdination number Ns of In melt decrease with increasing temperature from 280 to 750℃. The viscosity of In melt drops as temperature increases and meets on the whole the whole the exponential relation. Thermal contraction of atom clusters can be found in the heating process. The sudden change in structure or noticeable contraction occurs in the range of 390-550℃. The anomalous change of viscosity is measured at about 430 and 470℃, which is in good accordance with that of structure. A theoretical discussion on the correlation of struture and viscosity of In melt is given in this paper.