To reveal the surface forming law of electrochemical machining (ECM), an electric-magnetic-heat-flow multi-physical field coupling micro-material simulation model was established to dynamically track the forming process of anode micro surface from several aspects, such as current density distribution, roughness and micro-morphology. The dynamic evolution law and influencing mechanism of Ti-48Al-2Cr-2Nb alloy under different magnetic field conditions were revealed, and the simulation results were verified by electrochemical machining experiments. The simulation show that the forming of ECM surface is a complex competitive process of the formation and dissolution of surface film, and the micro-surface repeatedly goes through coarsening and polishing stages during the machining process. Surface roughness is 0.121 μm and spectrum area of multifractal spectrum is 0.0030 without magnetic field, while the surface roughness is 0.118 μm and the spectrum area is 0.0023 with magnetic field. The experimental results of ECM confirm that the surface roughness is 1.16 μm, the spectrum width of multifractal spectrum is 0.87 and the spectrum area is 1.468 without magnetic field, while the surface roughness is 0.93 μm, the spectrum width is 0.84 and the spectrum area is 1.388 with magnetic field. The simulation results agree well with the experimental results, the magnetic field reduces the machined surface roughness, makes the microstructure simpler and more uniform, and improves processing stability.