Abstract: The spacecraft sine vibration test can be used to reveal multiform dynamic characteristics, so a model updating method based on the sine vibration response data is important. The model reduction is necessary in an incomplete test data process. Firstly, the Guyan reduction method and the IRS reduction method are compared to show their merit/defect and application range. Secondly, an updating method based on excitation response data is derived by using the reduced model. Lastly, the unitary non-updated parameters are updated based on the incomplete test data of the GARTEUR. The results show that the IRS reduced updated model performs good in calculating/predicting the modes in/outside the updating frequency range with favorable results of response updating.