Abstract: To consider the uncertainty, a Sampled-Blind-Number (SBN) based static security evaluation for distribution networks is put forward. The load and distributed generation are modeled as a region load with uncertainty and it is described by a certain SBN with a group of sampled values and the corresponding probabilities. A fault is set in each position and N-1 criterion is checked for each combination of the possible load value. The risk probability of N-1 criterion not met, the degree of risk and the safety margin from risk are calculated. An example is given to explain the proposed approach showing the SBN is a good way to describe random load with arbitrary probability density function and the static security assessment considering uncertainty is referable for the expansion planning of distribution networks.