The invention provides a posture adjustment assembly system used for butt joint of components of a rocket. The posture adjustment assembly system comprises a posture adjustment system, a test system and a controller, wherein the posture adjustment system comprises first guide rails, beams and guide rail wheels, the guide rail wheels can move along the first guide rails through a horizontal moving mechanism, the posture adjustment system further comprises two posture adjustment devices arranged in parallel, each posture adjustment device is transversely arranged on the upper sides of the two first guide rails and is connected with the top faces of the beams, and each posture adjustment device comprises a supporting beam, a lifting table, a bracket support and an arc-shaped bracket. A posture adjustment method of the posture adjustment assembly system used for butt joint of the components of the rocket includes six steps. The posture adjustment system comprises the two posture adjustment devices, and the test system comprises an optical measurement device, measurement points located at the end of a rocket body and a processor. When only one single posture adjustment device is combined with the first guide rails, the guide rail wheels and the horizontal moving mechanism, four-freedom-degree posture adjustment can be achieved; when the two posture adjustment devices are used in cooperation with each other, six-freedom-degree posture adjustment can be achieved, and the two posture adjustment devices are independent, do not interfere with each other during six-freedom-degree adjustment and are matched with each other during adjustment.