In order to improve and strengthen the performance of giant magnetostrictive materials (GMM), the basic principles of optimization and design are provided that is small magnetic leakage, high magnetic intensity and superior uniformity on the centerline of the GMM rod before analyzing working principle of giant magnetostrictive actuator (GMA) and characteristics of GMM. The laws existed between structural parameters of the key magnetizer and magnetic circuit have been achieved based on Ansoft Maxwell electromagnetic finite element analysis. The cause of these laws has also been revealed by Gaussian flux theory. Then the key structural parameters are all designed and optimized and applied into the GMA. The experiment result indicates that magnetic intensity on the centerline of the GMM rod is raised from 55.4 kA/m to 70.35 kA/m and growth is 26.98%, the uniformity near the GMM rod is increased from 44.22% to 99.5%. The study shows that the permeability cover is mainly to reduce magnetic leakage, improve the intensity of magnetic field and too big or small diameter and thickness will lead to more leakage, U magnetizer is mainly to perfect the magnetic field and improve the uniformity.