A　novel　gray-level　image　encryption/decryption　scheme　is　proposed,　which　is　based　on　quantum　Fourier　transform　and　double　random-phase　encoding　technique.　The　biggest　contribution　of　our　work　lies　in　that　it　is　the　first　time　that　the　double　random-phase　encoding　technique　is　generalized　to　quantum　scenarios.　As　the　encryption　keys,　two　phase　coding　operations　are　applied　in　the　quantum　image　spatial　domain　and　the　Fourier　transform　domain　respectively.　Only　applying　the　correct　keys,　the　original　image　can　be　retrieved　successfully.　Because　all　operations　in　quantum　computation　must　be　invertible,　decryption　is　the　inverse　of　the　encryption　process.　A　detailed　theoretical　analysis　is　given　to　clarify　its　robustness,　computational　complexity　and　advantages　over　its　classical　counterparts.　It　paves　the　way　for　introducing　more　optical　information　processing　techniques　into　quantum　scenarios.