The　algorithm　for　three-dimensional　information　encryption　based　on　the　phase　extraction　is　proposed.　The　three-dimensional　information　with　the　pure　amplitude　and　pure　phase　are　constructed　as　the　encryption　target.　First,　the　complex　amplitude　of　the　three-dimensional　information　is　calculated　under　the　scalar　diffraction　theory.　Then　its　phase　distribution　is　extracted　independently　and　it　is　encrypted　with　the　double　random　phase　encoding.　The　decryption　algorithm　is　just　the　inverse　process　as　the　above.　Computer　simulation　demonstrate　the　feasibility,　the　robustness　and　the　security　of　the　algorithm.　Further,　it　is　revealed　the　potential　of　applying　the　algorithm　for　the　three-dimensional　information　encryption　with　much　larger　information　quantity.