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Topographical factor is one of the most important factors in understanding the formation mechanism of shallow mass movements on gully slopes on the Loess Plateau, China. However, the sensitivity of shallow mass movements on gully slopes to topography is poorly understood. Here, a series of rainfall simulation experiments was performed to quantitatively explore the influences of slope height (1.0 and 1.5 m) and gradient (60° and 70°) on shallow mass movements on the natural loess slopes on the Loess Plateau. Our research observed shallow mass movement processes on undisturbed slopes by using a Topography Meter and collected data that well reflected the nature of the processes. The conducted study has advantageous over traditional methods that are usually used in laboratory tests of backfilled soil. Results showed that the amount of shallow mass movement increased with increased slope height and gradient. The shallow mass movement rates (i.e., gravity erosion rates) increased by approximately 3–8 times with increased slope height from 1.0 m to 1.5 m, and increased by 148%–525% with increased slope gradient from 60° to 70°. The sensitivity coefficient of slope gradients for shallow mass movements was 2.1 times larger than that of slope heights for the shallow mass movements. Slope heights had the greatest effect on earthflow relative to slide and avalanche, whereas slope gradients had the greatest effect on slide. Our results provided insights into natural hazard susceptibility assessment and control erosion processes.