According to the parameter-free first principles calculations, we investigate the spin polarized transport in antiferromagnetic spin valve (AFSV) based on noncollinear IrMn. The giant magnetoresistance (GMR) in Co/IrMn/Cu(111) with L12-type IrMn shows three-fold rotational symmetry, which is easy to be distinguished from the GMR of normal ferromagnetic spin valves. Moreover, GMR based on -phase IrMn with current-in-plane (CIP) structure shows that GMR is 7.7%, around two time larger than that in current-pendicular-to-plane (CPP) structure (3.4%). Our study demonstrates that the AFSV CIP structure possesses a larger GMR effect than the CPP structure, and the GMR effect in AFSV based on noncollinear antiferromagnetic structure is larger than that based on collinear antiferromagnetic structure such as FeMn.