To optimize the electromagnetic performance of giant magnetostrictive actuator(GMA), equivalent magnet circuit equation was proposed, and effects of magnetic circuit components gap's magnetic permeability and the evenness of driving magnetic field on the magnetic field characteristics were analyzed based on the equation. the driving coil's structure was designed, and its shape was optimized based on G-factor; with the electromagnetic field analysis function available in ANSYS program, several different magnetic circuits and their field distribution are analyzed. As a result, a kind of magnetic circuit structure with more even magnetic field is found out. The actuator prototype was made and tested, and result shows the optimal method proposed in the paper can greatly improve performance of GMA.