Abstract: Sm (Co_balFe_0.1Cu_0.1Zr_0.033)_7.5permanent magnets was prepared by powder metallurgy method with an addition of liquid phase La₃Co.The effects of La₃Co addition on the demagnetization curve, remanence, coercivity and mechanism of high temperature coercivity of Sm (Co_balFe_0.1Cu_0.1Zr_0.033)_7.5permanent magnets were studied.It was found that demagnetization curve was improved with La₃Co addition, due to the change of cell structure in the magnets.As the addition of La₃Co comes to 3%, the magnet achieves the best demagnetization curve, while as the addition of La₃Co comes to 5%, the demagnetization curve becomes deviation again.Remanence and magnetic energy product, which are intrinsic magnetic properties for the magnetic materials, decreased with La₃Co addition account to the La element is a non-magnetic element.The coercivity at room temperature decreased with the addition of La₃Co increasing, which account to the 1:5 cell boundary phase volume fractions increase.Coercivity mechanism of the precipitation-hardened Sm (Co_balFe_0.1Cu_0.1Zr_0.033)_7.5high-temperature magnets was described by the theory of single-phase permanent magnets.The addition of La₃Co reduce the exchange coupling between the cell body and improve the coercivity in high temperature of permanent magnet, when the addition of La₃Co come to 3%, the coercivity of the magnets at high temperature 500℃reaches 0.9T.