Abstract: The electromagnetic interference of shipborne moving equipments should be evaluated correctly, because it cannot be degaussed by traditional methods. Taken artilllery as an example, the finite difference time domain(FDTD) method was applied to analyze the changes of electromagnetic fields of the artillery with the gesture changing. The average electrical parameters were adopted to improve the model accuracy of metal equipments. By changing coordinates, the modified difference equations were proposed to modify the metal edges, which cannot match the Yee grids. The algorithm was proved effectively by example comparisons. At last, results indicated that the changes of electric fields are 0.6~3.8 V/m, and the changes of magnetic fields are 0.0016~0.01 A/m when the gesture of the artillery changes. The influences of these kinds of electromagnetic changes to ship electromagnetic compatibility cannot be ignored.