A　single-shot　dual-wavelength　digital　holographic　microscopy　with　an　adjustable　off-axis　configuration　is　presented,　which　helps　realize　real-time　quantitative　phase　imaging　for　living　cells.　With　this　configuration,　two　sets　of　interference　fringes　corresponding　to　their　wavelengths　can　be　flexibly　recorded　onto　one　hologram　in　one　shot.　The　universal　expression　on　the　dual-wavelength　hologram　recorded　under　any　wave　vector　orientation　angles　of　reference　beams　is　given.　To　avoid　as　much　as　possible　the　effect　of　zero-order　spectrum,　we　can　flexibly　select　their　carry　frequencies　for　the　two　wavelengths　using　this　adjustable　off-axis　configuration,　according　to　the　distribution　feature　of　object＇s　spatial-frequency　spectrum.　This　merit　is　verified　by　a　quantitative　phase　imaging　experiment　for　the　microchannel　of　a　microfluidic　chip.　The　reconstructed　phase　maps　of　living　onion　epidermal　cells　exhibit　cellular　internal　life　activities,　for　the　first　time　to　the　best　of　our　knowledge,　vividly　displaying　the　progress　of　the　nucleus,　cell　wall,　cytoskeleton,　and　the　substance　transport　in　microtubules　inside　living　cells.　These　imaging　results　demonstrate　the　availability　and　reliability　of　the　presented　method　for　real-time　quantitative　phase　imaging.　(C)　2021　Optical　Society　of　America