Space-time adaptive processing(STAP)technique can mitigate airborne radar clutter and detect moving targets effectively. Based on adaptive radar theory, the Degrees-of-freedom(Do F) of a STAP processor should be larger than that of the received clutter. The local-Do Fs of clutter for Reduced-dimensional STAP(RDSTAP) methods with sparse linear array are studied. The proposed formulas show that the local-Do Fs of clutter can be estimated as the product of the equivalent clutter bandwidth with the equivalent sampling interval. Based on adaptive radar theory, the Degrees-of-freedom (Do F) of a STAP processor should be larger than that of the received clutter. The local-Do Fs of clutter for Reduced-dimensional STAP (RDSTAP) methods with sparse linear array are studied. The proposed formulas show that the local-Do Fs of clutter can be estimated as the product of the equivalent clutter bandwidth with the equivalent sampling interval.