Observability analysis is the basic and prime task in passive localization and tracking system, for only when the system is observable, it can be determined with unique and definite solution. In this paper, the observability for two kinds of typical maneuvering motion (constant acceleration and constant turn rate motion) is analyzed from the perspective of linear system theory, utilizing the integrated information of target's angle of arrival and Doppler frequency. This may lay the theoretic foundation for further research of maneuvering target localization and tracking. Finally, two simulation instances are presented to demonstrate the mathematical derivation and the results are consistent with those concluded from theoretic analysis, indicating that the method is correct and valid.