In this paper, a kind of Stack Giant Magnetostrictive Actuator (SGMA) was designed, then the magnetic field distribution model of SGMA was established, and analytical research on model was conducted to increase uniformity of bias magnetic field of GMA. Firstly, given the characteristics and drawbacks of infliction way of bias magnetic field in traditional GMA, structural form of alternative arrangement for permanent magnet and GMM rod was adopted to design SGMA. Then by combining magnetic circuit model with Biot-Savart law, magnetic distribution model can accurately describe magnetic feature of SGMA was establish. Subsequently, the influence of different parameters on magnetic field distribution feature was analyzed on established model, and structural design method of SGMA was proposed. Finally, model verification experiments were conducted. The result indicates: maximum relative error is lower than 4% when using established model to describe magnetic field distribution of SGMA; maximum relative error is lower than 5% at the time of predicting output displacement of SGMA. The established model in this paper can describe work state of SGMA accurately, increase system precision of SGMA and provide reference basis for structural design of SGMA.