On the basis of measuring the viscosity of Sn melt and referring to analysis of high temperature XRD, the change of viscosity and structure for Sn melt with temperature were carried out. The results show that there is discontinuous change of viscosity for Sn melt with the temperature. The state of Sn melt are divided into high, middle and low-temperature region according to the change of viscosity, and there is an anomalous point of viscosity change between different temperature region. There is a correlation between the viscosity change of and the structure change of Sn melt. The coordination number and correlation radius, and the fluid cluster size of Sn melt decrease with the increase of temperature, so that the viscosity of Sn melt decrease. But there is an anomalous change in the vicinity 673 K and 1073 K, it results in discontinuous change in viscosity of Sn melt.