Abstract: Through the moving coordinates and the perturbation analysis of boundary layer of wave front‚the linear relationship between the normal velocity and the wave-front curvature and the external field‚that is‚the Eikonal equation in external field‚was obtained．The physical meaning of this relationship can be used to explain the Belousov-Zhabotional experimental phenomenon of spiral wave and scroll wave affected by external field‚while the geometric meaning of it is to give a theoretic method to determine the shape of wave-front boundary．

Key words: exciting media, wave front curvature, external field, spiral wave, scroll wave