Based on the mcchanical theory and theoretical analysis, a two-phase (gas-liquid or gas-solid) flow's separation vane is designed. A functional expression with twophase flow's separation efficicncy as an objective function is constituted. A conclusion that the value of separation efficicncy is conccrncd only with the cxit reflective angle of vane is reached. In virtue of the conclusion, a two-phase flow's separation vane can be designed in a more scientific and reasonable way.