In order to understand the effects of Re and Ru additions on solidification characteristics of nickel base single crystal superalloys, four nickel base single crystal superalloys containing different contents of Re and Ru, were produced by dual heating zone melting and liquid-metal cooling (LMC) directional solidification technique at the withdraw rate of 2 μm/s, and a planar solid/liquid interface was obtained. The equilibrium partition coefficients of each element and solidification characteristic temperatures of experimental alloys were also obtained. Results show that with the increasing of Re content, the segregation degree of high segregation elements Re, W and Ta decreases, the liquidus temperature decreases initially and then increases, while the solidus temperature decreases continuously. The addition of Ru has little influence on the partition of other elements, and slightly lowers the liquidus temperature and solidus temperature of superalloys. In addition, we can effectively forecast the segregation degree of elements and solidification defects of non-equilibrium directional solidified superalloys on the basis of equilibrium partition coefficients and solidification characteristic temperatures