The theory of detecting target for stepped-frequency continuous wave radar is introduced in this paper and the signal processing of stepped-frequency continuous wave which uses the sampling frequency follows method is presented. Aiming at the problem of velocity-frequency coupling and velocity-range disorder caused by target moving, the same target has same digital Doppler frequency signal through using this method. Then, though compensating every phase of Doppler frequency of stepped-frequency signal, we can obtain a precision range-velocity image. Therefore, the sampling frequency follows method is a 2D range-velocity detecting method of moving target.