The China-Pakistan Economic Corridor is the flagship project of the Belt and Road Initiative. Rainfall erosivity is an important indicator to evaluate the carrying capacity of regional resources and environment. Estimation of the overseas high spatial resolution rainfall erosivity is significant to the construction of the China-Pakistan Economic Corridor. In this paper, rainfall erosivity of Pakistan in 2010 was estimated with TRMM 3B42 data, and a spatial downscaling algorithm based on the relationships between rainfall erosivity and relevant environmental factors such as meteorology, topography, and vegetation was proposed. By applying the spatial downscaling algorithm, the spatial resolution of rainfall erosivity was improved to 1 km. The results were as follows: (1) The rainfall erosivity simulated by the spatial downscaling algorithm displayed a significant correlation with the rainfall erosivity estimated from TRMM 3B42 data (R2 = 0.94), suggesting that the simulated rainfall erosivity by spatial downscaling algorithm could reflect the spatial distribution of rainfall erosivity effectively, especially in the northern mountains and east edge of the Baluchistan Plateau. (2) The rainfall erosivity of Pakistan in 2010 varied from 0.58 to 5 929.85 (MJ·mm)/(hm2·h·a), and the average value was 524.15 (MJ·mm)/(hm2·h·a). The spatial distribution of rainfall erosivity was high in the east and low in the west, and the areas with high-value of rainfall erosivity were mainly located in the vicinity of Islamabad, Mankera, Sialkot-Lahore-Sahiwal, and Karachi.