To solve the difficulty of analyzing the observability of fixed single station passive location in strongly nonlinear systems,an analysis method based on linear system observability theory is proposed.Taking the target azimuth,azimuth change rate and Doppler frequency change rate as observations,the complex Jacobian matrix is avoided by pseudo-linearization of the observation equation.Observable analysis of uniform velocity,uniform acceleration linear motion and uniform turning motion leads to observable conditions and provides theoretical premise for further research.Simulations examples are given to verify the correctness of the theoretical analysis of observability.