The invention discloses a design method for a recess width variable MTD filter based on prior information. The method comprises the steps of 1) searching parameters; 2) obtaining a covariance matrix of ground clutters; 3) obtaining initialized interference signal power; 4) designing an FIR filter of a digit integrated method; 5) searching a power spectrum variance of the ground clutters; 6) obtaining an FIR filter of an optimal clutter improvement factor; and 7) designing the recess width variable MTD filter. According to the invention, the prior information of a radar surrounding scene is obtained, so that the clutter improvement factor of the output end of the filter is kept optimal. The problem that the recess width in the zero frequency position of the MTD filter is fixed in the prior art is solved. The MTD filter designed in the method has different expected recess widths for different central frequencies, and detection for low-speed movement objects is enhanced.