We have investigated the relationships between electric field-induced resistance change and the magnetic properties of the Cr₂O₃/ultra-thin La_0.7Sr_0.3MnO₃ (LSMO) magnetic hetero structure. The LSMO with a thickness of 40 nm has two transition temperatures, the ferromagnetic Curie temperature of 312 K and the spin-glass temperature of 180 K. Resulting from the magnetic properties, the exchange interaction in the Cr₂O₃/LSMO behavior below 180 K differed from that below 312 K. With the application an electric field on the Cr₂O₃ gate, the resistance of LSMO film was changed. This resistance change is most likely due to the magnetic state of LSMO and the interface interaction between the Cr₂O₃ and LSMO film