A method and system for assessing the risk of the connection of photovoltaic power generation to a distribution network are provided. The method comprises selecting, in pre-divided photovoltaic powergeneration clusters, a photovoltaic power generation node at random as a primary node; calculating, based on the photovoltaic power generation cluster and the primary node, the cumulative distributionfunction of the primary node voltage and the cumulative distribution function of a branch power flow; based on the cumulative distribution function of the primary node voltage and the cumulative distribution function of the branch power flow, calculating the voltage out-of-limit risk index of the distribution network and the branch power flow out-of-limit risk index of each photovoltaic power generation cluster. The method divides the large-scale distributed photovoltaic power generation into the photovoltaic power generation clusters, and takes account of the correlation between photovoltaicpower generation and loads, thereby overcoming the defects that the multi-node risk index cannot be calculated, improving the accuracy of probability power flow distribution, calculating the voltageout-of-limit risk index of the distribution network voltage based on the risk index of each node, and improving accuracy of assessment.