A new technique was presented for adjusting the playback wavelength of Lippmann holograms recorded in methylene-blue sensitized dichromated gelatin(MBDCG). The main feature of this technique is introducing a water-soluble organic reagent into MBDCG photosensitive layer as preswelling reagent and wavelength adjuster. This method has wide wavelength adjustment range (up to 200 nm) and high signal-to-noise ratio, can be applied to quantitatively adjust the playback wavelength of reflection hologram by changing the concentration of preswelling reagent. Its possible applications include color image display, holographic optical elements, and optical anti-counterfeiting.