The key encapsulation mechanism (KEM) and the data encapsulation mechanism (DEM) form a hybrid encryption, which effectively solves the problem of low efficiency of public key cryptography and key distribution problems in symmetric encryption system. The security and efficiency of the key encapsulation mechanism directly affect the security and efficiency of hybrid encryption. In this paper, an identity-based key encapsulation scheme is constructed by using multilinear mapping. We proved that the scheme is under the standard model of adaptive chosen-ciphertext security. The scheme can be publicly verified and the key and ciphertext length are constant and have high efficiency.