The purpose of analysis on observability of the system is to estimate the efficient of Kalman filter. This paper sets up the mathematical model of Strapdown Inertial Navigation System and Global Positioning System integrated system (SINS/GPS), and then investigates the observability degrees of SINS/GPS basing on singular value decomposition and the method of the eigenvalues and eigenvectors. The simulation shows that the two methods are all effective to find out the unobservable states and their characters are very different, consequently establishing the academic base for further study on a fast and precise initial alignment method for the SINS/GPS.