  A novel U(1) topological gauge field theory for topological defects in liquid
crystals is constructed by considering the U(1) gauge field is invariant under
the director inversion. Via the U(1) gauge potential decomposition theory and
the $\phi$-mapping topological current theory, the decomposition expression of
U(1) gauge field and the unified topological current for monopoles and strings
in liquid crystals are obtained. It is revealed that monopoles and strings are
located in different spatial dimensions and their topological charges are just
the winding numbers of $\phi$-mapping.
