To know the effect of friction on the frequency response of Scanning Mirror System(SMS) in an aerial camera and to provide a model for describing the real dynamic of the SMS more exactly, the random phase multi-sine exciting signal was used to detect the feature of frequency response of the SMS and to identify a linear approximate parameter model. Firstly, the experiment setup for SMS identification was introduced and the exiting signal was selected. Then, the odd-odd frequency random phase multi-sine signal was used to measure the dependence of output of system at the non-exited frequency and exited frequency on the input signal, and to evaluate the nonlinear effect of friction quantitatively. Finally, an estimation method based on the sample mean value of signal and sample noise (co-)variances was used to identify the linear approximate parameter model of SMS. The experimental results indicate that the friction nonlinearity in the SMS is mainly located at the odd frequency, 10 dB above the noise. The frequency response of SMS varies under the different amplitudes of input signal, and the difference is obvious especially below 20 rad/s. Because of the effect of friction, the SMS should be described by a 3-order parameter model. Compared with sine-swept method, the parameter model based on multi-sine signal is better in describing the real dynamic feature of the SMS. Obtained results can provide the base for designing of controllers.