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A novel motion compensation method based on two-dimensional time-domain correlation (2D-TC) function for stepped-frequency radar (SFR) is proposed to focus the range profile of SAR image in the condition of high target speed and low pulse repetition frequency (PRF). In such condition, serious pulse-to-pulse envelope shift of SFR echo greatly decreases the velocity-estimation performances of traditional motion compensation methods. The 2D-TC function of two returned bursts is insensitive to envelope shift, which indicates the target migration proportional to the target velocity in both the high and the low range resolution dimensions. Using a target model composed of multiple scatterers, the auto and the cross components of the 2D-TC function are deduced. The performance of joint velocity estimation using both dimensions is analyzed, which results in higher accuracy and wider unambiguous extent for highspeed target and low-PRF waveform. Statistical tests of typical methods are simulated and compared, and the results verify the validity of the new method.