By using HSC-OTT Persivel32 laser raindrop spectrum detector (Germany), raindrop size distribution under natural rainfall was detected in Nanxiaohegou basin of Jinghe River, and the characteristics and distribution of raindrops in different kinds of natural rainfall were analyzed. The relationships among the elements of rainfall characteristics were analyzed as well. Results showed that: (1) The raindrop diameter of natural rainfall was concentrated at 0.3～1.5 mm in the study area, and this result was basically identical with that on the Loess Plateau which determined by the method of traditional filter paper splash. But the raindrop diameter was smaller than those in Northeast and Minnan region. The median raindrop diameter (D50) increased with the increase of rainfall intensity when rainfall intensity (I) was less than10 mm/h. When rainfall intensity was greater than or equal to 10 mm/h, the median raindrop diameter (D50) dropped abruptly, to some extent, it was related to rupture of large raindrops after the increase of rainfall intensity. The variation of rain spectrum with rain intensity in this area could be fitted by Best distributed. (2) The distribution curve of raindrops number with the diameter was flat in common rainfall, and its kinetic energy was linearly correlated with rainfall intensity, while the distribution curve of raindrop number with diameter in short formation rainfall was steeper, and its kinetic energy and rain intensity were power function. The rainfall kinetic energy increased with the increasing of rain intensity in both kinds of rainfall, but the kinetic energy of short formation rainfall increased faster, therefore short formation rains were more erosive.