A　method　to　optimize　the　shape　of　pole　is　presented　for　permanent-type　nuclear　magnetic　resonance　(NMR).　An　implicit　interface　representation　depicts　the　interface　by　means　of　level　set　function.　The　velocity　of　each　point　on　the　implicit　interface　is　given　with　the　continuum　shape　sensitivity　analysis,　the　evolution　of　this　level　set　is　controlled　by　a　Hamilton-Jacobi　equation　which　is　solved　by　using　finite　difference　scheme.　The　design　result　shows　the　effectiveness　of　the　proposed　algorithm.