  We investigate the 1/2-BPS Wilson-'t Hooft loops in ${\cal N}=4$
Super-Yang-Mills theory. We use the bulk D-brane with both electric and
magnetic charges to calculate the all genus contribution of the circular loops.
The expectation value of Wilson-'t Hooft loops are in perfect agreement with
the result through supersymmetric condition and duality transformation in the
gauge theory.
