Abstract: Attempts were made to define biodiversity risks, analyze their sources, work out principles and hierarchy for establishment of a biodiversity risk assessment index system and then to build up the system. Biodiversity risk assessment was performed of 2376 county-level administrative units, all over China. Results show that generally R (risk value) varies in the range between 0.0059 and 0.8283, and is less than 0.3 in most areas. High risk areas are located mostly in Guangxi, Yunnan, Sichuan, etc., with R being higher than 0.3291, while low risk areas are distributed mainly in Inner Mongolia, Shanxi, Shaanxi, etc., with R being lower than 0.0568, and moderate risk areas in Northeast China and North China. In the areas, the most abundant in biodiversity (T_S≥0.2958), there are still 38 county-level units moderate in R, owing mainly to the greater area of nature reserves and smaller pressure, with average E_R being 0.2906, and average R_P being 0.1423. However, in the areas, the poorest in biodiversity (T_S≤0.0502), although there are 22 units with R_P being quite high and with 0.4704 on average and 145 units that do not have any nature reserve, while as a whole their R are not so high, with average being 0.0570 and 0.0481, respectively.