In this paper,authors break throush the restriction of traditional meth-ods,new model structure determination approach based on multi-collinearity diagnos-tics,main components regression and choosing variables using main components analy-sis is proposed. Furtherly,the relationship among the new MSD approach,optimal in-put design and parameter identifiability are discussed.Its application to a controlledflight vehicle indicate that the new MSD is very dffective.