In　this　paper,　dual-wavelength　digital　holography　is　demonstrated　by　both　numerical　simulation　and　experiment.　Simulations　were　done　for　two　wavelengths　of　500　nm　and　550　nm.　The　objects　are　a　wedge　prism　with　a　height　of　2.5　mu　m　and　four　abrupt　steps.　Three-dimensional　(3D)　reconstruction　profiles　of　the　original　objects　are　obtained　in　the　simulations.　We　find　that　dual-wavelength　phase　unwrapping　is　a　fast　and　robust　method　for　removing　2　pi　discontinuities　compared　to　software　algorithm-based　methods.　In　the　experiment,　two　lasers　of　the　different　wavelengths　632.8　nm　and　671　nm　are　used　to　obtain　a　larger　beat　wavelength.　The　object　is　a　phase　grating.　In　dual-wavelength　phase　unwrapping,　two　individual　phase　images　are　obtained　by　using　each　wavelength,　respectively,　and　the　phase　image　for　beat　wavelength　is　obtained　by　subtracting　one　single　wavelength　phase　image　from　the　other　and　then　adding　2p　whenever　the　resultant　value　is　less　than　zero.　In　the　final　synthetic　image,　3D　profile　of　the　phase　grating　is　obtained　after　removing,　the　discontinuities　by　reducing　the　noise　of　the　beat　wavelength　phase　image.　The　experiment　results　demonstrate　the　effectiveness　of　the　dual-wavelength　phase　unwrapping　in　digital　holography.