The motion of the variable vane assembly of turbo-shaft engine is complicated.The kinetic equation of variable vane assembly was deduced using the method of homogeneous coordinates analysis and Matlab software.The dimensions of variable vane assembly components were optimized.This newly developed method was applied to the design of an engine's variable vane assembly.The calculated results were compared with the simulation result of CATIA.It shows the accuracy of control satisfies the design requirement.