  we present a new topological invariant to describe the space-time defect
which is closely related to torsion tensor in Riemann-Cartan manifold. By
virtue of the topological current theory and $\phi$-mapping method, we show
that there must exist many strings objects generated from the zero points of
$\phi$-mapping, and these strings are topological quantized and the topological
quantum numbers is the Winding numbers described by the Hopf indices and the
Brouwer degrees of the $\phi$-mapping.
