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The cast samples of low-alloy bainite wear-resistant cast steel of 20MnCrNi2Mo with anthanum-cerium mischmetal were tempered at 200, 250, 300, 350, 400, 450, 500, 550, 600 and 650 ℃ respectively for 1 h. The microstructure was observed by QUANTA-400 environmental scanning electron microscope and JEM-2100 transmission electron microscope, the precipitation was qualitatively and quantitatively analyzed by using physicochemical phase analysis, and the retained austenite after different temperature tempering was measured quantitatively by D8 ADVANCE X ray diffracmeter. The microstructure evolution during the tempering was investigated. The results show that the microstructure of the tested steel as cast is granular bainite. The precipitated equilibrium-phase carbide during the tempering is alloying cementite with trace amount of solid-solution rare earth. The recovery has not been found during tempering at 500 ℃. The subgrains are found become distinctly and the recovery is observed clearly during tempering at 650 ℃. The M/A islands do not decompose tempered at 200 ℃, with the increase of the tempering temperature, the M/A islands gradually decompose, and the amount of the M/A islands decreases so obviously that it can not be detected when the tempering temperature is up to 450 ℃.