The accumulation of progressive deterioration of structures might lead to the failure of structures. In order to avoid potential accidents, it is important to carry out condition assessment using structural system identification. This is based on the assumption that damage of structures can be reflected in the change of parameters. In every SSI method, measurement errors are introduced in the process of data collection and simulation errors also exist due to the inherent property of the algorithm used. The observability method has been proposed to deal with structural system identification under static loadings. Up to now, error analysis for this method has not been addressed yet. To fill this gap, this paper evaluate the effects of measurement errors and simulation errors on the observability method. The effects of measurement errors in a specific measurement and in all measurements are considered. The result indicate that the loading case and the location of the measrement is of primary importance. Also, rotations are less sensitive to errors than vertical deflections. On the other hand, the error propogation during the identification regarding the recursive steps and the curvature of structure is also illustrated.