The invention provides a quantitative evaluation method for the security risk of the operation of a power network. The method comprises the following steps: establishing a risk evaluation model, wherein the risk value of the power network is equal to a product of a consequence value and a probability value; determining the category of influence divisor items needing to participate in risk evaluation, and obtaining the weight value between influence divisor sub-items contained by each screened influence divisor item; according to harmful factors of the power network needing assessment, selecting corresponding influence divisor sub-items from each influence divisor item participating in the risk assessment, multiplying the selected influence divisor sub-items to obtain the probability value, and multiplying the probability value with the consequence value to obtain the risk value of the power network when the harmful factors occur in the power network. The method disclosed by the invention has higher scientificity and higher accuracy of the risk assessment, and reasonable quantitative evaluation can be performed on the risk and can be used as an objective measurement basis for guiding the actual production of electric power.