In order to improve the magnetic focusing performance of coil and expand the application of coil function, the 8-shaped coil is improved. And the main variable parameters of the coil are optimized through a hybrid optimization algorithm. And 8-shaped coils with different sizes are obtained. The coil simulation model is established, and the focusing and functional effects of the optimized 8-shaped coil are analyzed through optimization simulation. An experimental model consistent to the simulation model is built, and the simulation results are verified by using a uniform steel plate with 1 m of length, 1 m of width, and 5 mm of thickness and a solid conduit. The effectiveness of theoretical simulation is proved through comparison function. The improved 8-shaped coil model with different sizes can realize multi-function application. Under certain focusing, the coil can be flexibly applied to Helmholtz coil, Transcranial Magnetic Stimulation(TMS) coil array model and Functional Magnetic Stimulation(FMS) coil array.