The invention discloses a rotary seal device for a steel continuous casting machine. The rotary seal device comprises a shell, a seal ring A, a seal static ring, a seal movable ring, an elastic synchronizing pin, an elastic compensating set, a seal ring B, a thrust ball bearing, a locating sleeve, a fastening screw, an oilless bearing, a hole-use elastic stop ring, a parallel stop piece, a shaft-use elastic stop ring and a rotary shaft. The elastic compensating set is fixedly installed on one side of the shell. The seal static ring and the seal movable ring arranged on one side of the seal static ring are arranged on one side of the top of the elastic compensating set. The seal ring A is installed on the other side of the seal static ring. The elastic synchronizing pin is installed on one side of the top of the seal movable ring and is fixed to the shell. According to the rotary seal device, the oscillation adaptability and high temperature resistance of the whole movable rotary seal device are improved through material change and structure change, thus service life of the movable rotary seal device for the steel continuous casting machine is prolonged, maintenance cost is lowered, and economic benefit is increased.