The utility model relates to a converter steelmaking tapping slag blocking device which comprises a control mechanism, a converter mouth platform arranged on one side of a converter mouth, a slag blocking trolley installed on the converter mouth platform and capable of moving on the converter mouth platform, and a driving mechanism driving the slag blocking trolley to move. The slag blocking trolley is connected with the electromagnet through a connecting rod, and a slag blocking mechanism is attracted to the electromagnet; The slag stopping mechanism comprises a guide rod, a pig iron block fixedly connected to the upper end of the guide rod and a power-assisted guide block connected to the lower end of the guide rod, and a slag stopping plug is installed in the middle of the guide rod. The slag stopping mechanism has no delay during releasing, slag stopping work can be rapidly carried out, and the slag stopping efficiency of the device is improved; And the throwing accuracy of the slag stopping mechanism is high.