  We introduce a new entanglement measure based on optimal entanglement
witness. First of all, we show that the entanglement measure satisfies some
necessary properties, including zero entanglements for all separable states,
convexity, continuity, invariance under local unitary operations and
non-increase under local operations and classical communication(LOCC). More
than that, we give a specific mathematical expression for the lower bound of
this entanglement measure for any bipartite mixed states. We further improve
the lower bound for 2$ \otimes $2 systems. Finally, we numerically simulate the
lower bound of several types of specific quantum states.
