Abstract
This article proposed: The magnetic field is one of physical existence fundamental modes, it exists around the magnet around the space, the moving charge around the space as well as the electric current the space. The electric field and the magnetic field description depends on the electric charge speed, but speed with reference system related, thus it may be known, electric field and magnetic field description along with reference system's difference and difference. When an electric charge is opposite in some reference system static, observes in this reference system, another moving charge only receives this electric charge the electrostatic field function, not magnetic force. But observes in another reference system, this electric charge possibly is the movement, another moving charge besides receives this electric charge the electrical field intensity, meanwhile receives the magnetic field strength the function, to analyze the reason which the magnetic field strength produces, through coordinate transformation's way, strives for to enter the stage the first source electric charge in static reference system S ' the test charge receives electrostatic field strength; then transforms using the theory of relativity strength's transformation formula this strength S is, extracts the moving charge to the moving charge action, and summarizes the magnetic field strength essence from this.
Keywords：electric field magnetic field reference system special relativity conversion of coordinate
