Non-stationary signals generally refer to deterministic signals with time-variant energy spectrum or stochastic signals with time-variant power spectrum. Amplitude modulation is one of the forms of non-stationarities. The main objective of amplitude modulated signal analysis is to obtain the rule of amplitude variation. Based on the Hilbert square demodulation method and the “Hilbert Lowpass Filter” suitable for non-stationary signal recently discovered, the envelop is extracted from an amplitude modulated non-stationary signal. Numerical examples are given to illustrate the efficiency of this method.