Rheological behaviors of Sn melt were systematically studied using a comprehensive measurement instrument designed in our lab. Structure of the Sn melt was analyzed by a liquid XRD technology. The result indicates that in the vicinity of 400°C, 800°C and 1200°C, the melt is a non-Newtonian fluid, while it is a Newtonian fluid within the temperature ranges of 400—800°C, 800—1200°C and over 1200°C. It is evidenced that the rheological property of the Sn melt is correlated to the changes in the melt structure. When the temperature is raised, the correlation radius rc, the coordination number Ns decreases, while in the vicinity of 400°C and 800°C, the correlation radius rc and the coordination number Ns of the Sn melt all show discontinuous changes.