The invention discloses a device for controlling the posture of a projectile. The device for controlling the posture of the projectile comprises a guide rail; a groove is formed in the guide rail; a sliding strip is embedded in the groove; a thread channel is formed in the length direction of the sliding strip; the sliding strip is connected with a lead screw through the thread channel; a plurality of sawteeth are arranged sequentially on the upper surface of the sliding strip; the sliding strip is engaged with an incomplete gear through the sawteeth; the incomplete gear is connected to a fixing ring through two connecting rods; a rudder shaft is sleeved with the fixing ring; and rudder pieces are connected to the two ends of the rudder shaft correspondingly. Pneumatic control force is generated by changing the deflection angles of the rudder pieces, and the purpose of controlling the posture of the projectile is achieved, and the rudder pieces are simple in structure, convenient to mount and low in cost; and screw transmission and incomplete gear transmission are adopted, the structure is compact, response is rapid, transmission is efficient and accurate, and the constant instantaneous transmission ratio is achieved.