A new giant magnetostrictive actuator with displacement transmission mechanism was present to meet the requirements of the switching valve stroke. The distribution of magnetic induction intensity and elongation of the giant magnetostrictive actuator under different frequencies were studied. Electromagnetic computational model was established, and then the data obtained by ANSYS software simulation were imported into MATLAB for processing the images of different frequency magnetic field, and the average radial magnetic field was gotten by new way to calculate the elongation. The conclusions are: the eddy current effect increases and the magnetic induction density of the rod and cylinder will be reduced with the current frequency increases; the average intensity of the rod at both ends is low and the middle is high, while the cylinder is low when away from the output; the elongation of the rod is always higher than that of cylinder. These conclusions are of guiding significance during device design.