Abstract: With the increase of 3D printing applications in many areas of life, a large amount of 3D printing models is attacked and stolen by hackers. Moreover, some special models and anti-weapon models in 3D printing must be secured from un-authorized users. Therefore, 3D printing models should be encrypted before being stored and transmitted in order to prevent illegal copying. This paper presents an encryption algorithm for 3D printing models based on the edges of the interpolating tetrahedron. The proposed algorithm is based on encrypting the normal vector of facet and the edges of the interpolating tetrahedron by a secret key after the tetrahedron interpolation process. Each facet of 3D printing model is extracted to interpolate a tetrahedron, and the edges of the interpolating tetrahedron are then encrypted by a secret key. The encrypted edges of the interpolating tetrahedron and the encrypted normal vector are then used to generate the encrypted 3D printing model. Experimental results verified that the proposed algorithm is very effective for 3D printing models. The entire 3D printing model is altered after the encryption process. The proposed algorithm also provide a better method and more security than previous methods.