The invention provides a sleeve part device for a sitting posture correcting chair used for pupils. The device comprises a chair main body, side guide bodies and inner sliding chutes, wherein front and rear two parallel chair legs at the lower end of the chair main body are mortised through a fixing connecting rod, and inner sleeve support rods are fixedly connected to two ends of the connecting rod between the front and rear two chair legs. For the sleeve part device for the sitting posture correcting chair used for pupils, due to the arrangement of the inner sleeve support rods, inner rods and knee baffle blocks, when the inner rods are used, butting bolts can be loosened, so that the inner rods can move in the inner sleeve support rods, when the parts of the inner rods are not used, theparts of the inner rods can be just hidden below the chair main body, so that the normal use of the chair is not hindered, then the shank parts and the ankle parts of the pupil sitting on the chair can be inserted below the knee baffle blocks and a connecting rubber column, thus the legs are in the bent state, therefore, the upper part of the body is prompted to be straight, and finally, the sitting posture correcting is assisted.