Abstract: To improve the amplitude estimation accuracy of the fluctuating targets in clutter, an adaptive filter based on the cooptimized transmit-receiver with minimum Mean Square Error (MSE) criteria is proposed. The approach is performed in three stages. Firstly, the radar transmits a burst of probing signals to estimate the amplitudes of the out-of-window scatterers, and then the phase-modulated waveform for the next transmission is optimized adaptively based on the estimated information for sidelobe suppression of the large out-of-window scatterers. Finally, adaptive filtering for the echo signals is realized based on the statistical amplitude estimation of the scatterers in each range bin. The proposed method realizes a close-loop feedback system from the receiver and the transmitter. Moreover, it has better estimation accuracy and lower computational complexity in the filtering for the multiple echo signals. The effectiveness of the proposed method is verified by numerical simulation.