(Ni0.81Fe0.19)1-xCrx/NiFe/PtMn films were prepared by magnetron sputtering. The formation and thermal stablitity of NiFe/PtMn bilayers were systematically investigated. The experiment shows that the grain size of PtMn layer depends strongly on the change in Cr concent ration. Thermal stability of exchange bias indicates that (Ni0.81Fe0.19)1-xCrx/NiFe/PtMn films with larger PtMn grains have a higher blocking temperature, and the bigger grain size is helpful in reducing the critical thickness of PtMn layer, which is consistent with Mauri's model.