Abstract: An iterative model updating approach based on Cross Model Cross Mode (CMCM) method and Guyan model reduction method is proposed, which extends the CMCM method for the model updating by employing spatially incomplete modal data. The Constrainted Least Squares method is adopted in solving the CMCM equation to avoid possible negative stiffness and negative mass. A five-storey three-dimensional frame structure and an exsiting offshore platform structure were chosen as examples in the numerical study, and the study demonstrates that the method can effectively update a finite element model by employing spatially incomplete modal data, and the updated model is of good accuracy and keeps its physical connectivity.