The Cr poisoning effect on cathode is identified as a considerable negative factor for the long-term performance of Solid Oxide Fuel Cells(SOFCs). With the lowering of the operating temperature of SOFCs, more high performance cathode materials could be used. In this study, the relation between testing temperature of SOFC and the Cr poisoning effect on La_0.6Sr_0.4Fe_0.8Co_0.2O_3-δ - Ce_0.9Gd_0.1O_2-δ symmetric cells is investigated . Combined with the SEM and XRD , a secondary phase, identified as SrCrO₄ is found formed on the surface of cathode to cause serious cathode degradation. The EIS shows that as the increasing of performance temperature from 550°C to 750°C, the Cr poisoning effect firstly increases to the maximal poisoning effect on 650°C and then decreases as the increasing of testing temperature. The evaporation of Cr from metallic interconnect could increase with the rising of testing temperature, However , the surface incorporation and exchange of Cr or O₂ may not obey the tendency of temperature. With the DRT calculation, the Cr is more easily to occupy the Co sites on the LSCF but O is more tend to occupy the Sr sites, which may lead to the existence of the peak performance temperature for the remarkable Cr poisoning effect on LSCF.