In-situ observation of eutectic solidification of Cr12MoV steel was conducted using high temperature confocal laser-scanning microscopy. The semi-solid isothermal treatment temperature of the steel was determined by thermodynamic calculation using Thermo-cal software. At the same time, the infl uences of isothermal treatment temperature and time on eutectic carbides in the steel were also studied. The results show that when the liquid metal cools at the rate of 47 °C·min-1, the eutectic reaction occurs rapidly at 1,214.7 °C in one second with the reticular liquid around austenite dendrites, transforming into a network of eutectic structure. After being held at 1,300 °C for 30 min, the carbide network is broken due to the impingement of refi ned primary austenite dendrites and secondary dendrites arms, and the thickness of eutectic structure is reduced. In-situ observation of eutectic solidification of Cr12MoV steel was conducted using high temperature confocal laser-scanning microscopy. The semi-solid isothermal treatment temperature of the steel was determined by thermodynamic calculation using Thermo-cal software. At the same time, the infl uences of isothermal treatment temperature and time on eutectic carbides in the steel were also studied. The results show that when the liquid metal cools at the rate of 47 ° C · min-1, the eutectic reaction occurs rapidly at 1,214.7 ° C in one second with the reticular liquid around austenite dendrites, transforming into a network of eutectic structures. After being held at 1,300 ° C for 30 min, the carbide network is broken due to the impingement of refi ned primary austenite dendrites and secondary dendrites arms, and the thickness of eutectic structure is reduced.