The invention discloses a millimeter-grade micro-motion measuring method based on a synthetic broadband pulse Doppler radar. By employing the phase-deduction velocity and range measurement technology, the target movement is precisely measured, and an iteration motion parameter combined estimation method is employed to measure the target millimeter-grade micro-motion and extract target motion parameters precisely; compared with a conventional narrowband micro-motion measuring method, the millimeter-grade micro-motion measuring method is a phase-grade high-precision micro-motion measuring method, the range-measuring precision is the millimeter grade, the velocity-measuring precision is centimeter / second grade, and the requirement of high-precision range and velocity measurement of the radar for micro-motion extraction is satisfied; high resolution ability for the distance is provided, scattering points of a complex target can be separated, and distance and motion information of different scattering points of the target can be simultaneously obtained; the broadband PD processing method can realize echo coherent accumulation and effectively suppress static and low-speed clutters; and with the combination of track filtering information, the broadband enveloping range / velocity measurement precision can be improved, and the requirement of the signal to noise ratio by correct phase unwrapping is reduced.