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 simulations 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.