Abstract: When design an optimal control system,choosing a performance index is a important but not completely solved yet problem to the designers.Recently,a kind ofdesign idea to determine the performance index according to the expected closed-loop eigenvalues was proposed,and some corresponding algorithms were developed.In thispaper,this design idea and Seheim's algorithm which is easy to be implemonted on acomputer are introduced,and some further improvements on the algorithm are pressented.By the improved algorithm the closed-loop eigenvalues can be put closer to theexpected values than those from Seheim's,and it is simpler as well.As an application example,the optimal pole assignment method and the normal one are used todesign a longitudinal stabilization system of a helicopter respectively,and the two design methods are compared by digital simulation.