  Quantum nonlocal correlation (QNC) is thought to be more general than quantum
entanglement correlation, but the strength of it has not been well defined. We
propose a way to measure the strength of QNC basing on the characteristic
function. The characteristic function of QNC in a composite system is defined
as a response function under the local quantum measurement. It is explored that
once a characteristic function is given, the state of a composite system, with
just a local trace-preserving quantum operation uncertainty, will be
determined. We show that the strength of QNC basing on the characteristic
function is a half-positive-definite function and does not change under any LU
operation. For a two-partite pure state, the strength of QNC is equivalent to
the quantum entanglement. Generally, we give a new definition for quantum
entanglement using the strength function. Furthermore, we also give a
separability-criterion for 2\timesm-dimensional mixed real matrix. This letter
proposes an alternate way for QNC further research.
