Embodiments for filtering clutter signal from Doppler signal in an ultrasound system are disclosed. In one embodiment, a Doppler signal acquiring unit may transmit and receive ultrasound signals to and from a target object to acquire Doppler signal. A signal processing unit performs filtering upon the Doppler signal by using a first clutter filter having a first cutoff frequency and compute an input signal power to filtered input signal power rate (IFR) for the Doppler signal. The signal processing unit is further configured to be responsive to the IFR to modulate the Doppler signal and perform filtering upon the modulated Doppler signal by using the first clutter filter or to perform filtering the Doppler signal by using a second clutter filter having a second cutoff frequency.