The invention provides an automatic gun replacing device and an automated steelmaking system, and relates to the technical field of smelting. The device comprises a temperature measuring gun replacingpart and a sampling bar replacing part; the temperature measuring gun replacing part comprises a temperature measuring gun locating mechanism and a temperature measuring gun propelling mechanism; thetemperature measuring gun locating mechanism is used for accommodating a temperature measuring gun; the temperature measuring gun propelling mechanism is arranged at one side of the temperature measuring gun locating mechanism in the length direction and used for propelling the temperature measuring gun in the length direction of the temperature measuring gun; the sampling bar replacing part comprises a sampling bar locating mechanism, a sampling bar clamping and rotating mechanism and a sampling bar propelling set; the sampling bar locating mechanism is used for accommodating a sampling bar;the sampling bar clamping and rotating mechanism is arranged at one side of the sampling bar locating mechanism in the width direction, and used for clamping and horizontally placing the sampling barwhich is vertically placed in the sampling bar locating mechanism; the sampling bar propelling set is arranged at the other side of the sampling bar locating mechanism in the width direction and usedfor linearly propelling the horizontal sampling bar in the length direction of the sampling bar locating mechanism.