A matrix perturbation theory in structural dynamic design is presented in this book The theory covers a broad spectrum of subjects,the perturbaion methods of the distinct eigenvalues and repeated/close eigenvalues,the perturbation methods of the complexmodes of systems with real unsymmetric matrices,the perturbation methods of the defective/near defective systems,random eigenproblem and the interval eigenproblem for the uncertain structures.The contents synthesized the most recent research results in the structural dynamics.Numerical examples are provided to illustrate the applicationsof the theory in this book.This book is recommended to graduates,engineers and scientist of mechanical,civil,aerospace,ocean and vehicle engineering.