The density matrix renormalization group (DMRG) method was firstly developed by White to solve the strongly correlated quantum lattice models. Later, this method was introduced into the quantum chemistry to deal with the strongly correlated states in molecular electron structures, which helped DMRG method to stand out of other multi-reference methods by its attractive potential of handling large active space. A relatively large active space containing up to 108 orbitals 10 can be processed by the DMRG method, whereas the full configuration interaction (full-CI) method can only handle around 20 orbitals. This is because the computational cost of the full-CI method grows exponentially with the increase of the system size, resulting an unaffordable cost with this moderate size. On the other hand, the DMRG method holds a polynomial complexity of O(N 4 m 2 ) + O(N 3 m 3 ), where the N indicating the number of the correlated orbitals and the m (usually in a few hundreds or thousands) representing the bond dimension of the wavefunction tensors, making DMRG a more conspicuous method than other methods. However, the computational cost of the DMRG method is still very expensive for practical chemistry applications.