  In this Letter we find the new criteria of separability of multipartite qubit
density matrixes. Especially, we discuss in detail the criteria of separability
for tripartite qubit density matrixes. We find the sufficient and necessary
conditions of separability for tripartite qubit density matrixes, and give two
corollaries. The second corollary can be taken as the criterion of existence of
entanglement for tripartite qubit density matrixes. In concrete application,
its steps are quite simple and easy to operate. Some examples, discussions and
the generalization to more high dimensional multipartite qubit density matrixes
are given.
