This paper oriented to study hydrodynamic characteristics of steep loess slopes (25°~50°), in an attempt to lay down a foundation for elucidating the in-depth relationships of the hydrodynamic characteristics of shallow water flow on slopes with soil erosion. An indoor experiment was carried out to simulate rainfalls on steep loess slopes. The experiment was designed to have only one soil type (loessal soil), three rainfall intensities (1.0 mm/min, 1.5 mm/min and 2.0 mm/min) and six slope gradients (25°, 30°, 35°, 40°, 45° and 50°). Results showed that:(1) Soil erosion rate increased with rising rainfall intensities on slopes with the same gradient, and under the same rainfall intensity, the effects of slope gradients on soil erosion rate exhibited a critical point in gradient, that was, between 40° and 45°. On slopes with gradient lower than the critical point, soil erosion rate increased with rising slope gradients, whereas on slopes with gradient higher than the point, soil erosion rate decreased with rising slope gradients. (2) Flow shear stress, stream power and unit energy of water-carrying section were increased with the rising rainfall intensities and slope gradients, while stream power had the best regularity. (3) The increasing power functions were found between soil erosion rate with flow shear stress, unite stream power and unit energy of water-carrying section, with the determining coefficient of R²(ω)>R²(τ)>R²(E). So stream power was the best one of all the hydrodynamic parameters tested to describe the soil erosion process on the steep loess slopes.