The invention relates to the field of attitude control engines of rockets, in particular to an attitude control device and system using gas of a rocket engine. The attitude control device comprises atleast two engine units; each engine unit comprises a first engine, a second engine and a third engine; each first engine and the corresponding second engine are on the same straight line; and each third engine is perpendicular to the corresponding first engine. The attitude control system comprises a propellant storage box, a heat exchanger, a main engine, a buffering gas tank and an attitude control device; a propellant in the propellant storage box enters the main engine through a loop of the heat exchanger; gas discharged from a gas interface of the main engine enters the buffering gas tank through another loop of the heat exchanger; and the buffering gas tank communicates with the attitude control device. The attitude of a rocket can be controlled flexibly to fulfill functions of pitching, rolling and yawing; and manufacturing and mounting can be facilitated. The invention is also an optimal layout scheme by which the total weight of the system is light.