The invention relates to an electric power system safety assessment system based on a risk theory; the electric power system safety assessment system comprises a power grid topology structure parameter input module, a history statistics element outage failure rate input module, a system state selection module, a load flow calculation module, a fault accident result severity calculation module and a risk assessment module; the electric power system safety assessment system can effectively solve the disadvantages of a conventional assessment method, fully considers fault accident happen probability and result severity, thus more reasonably and fully describing the electric power system risk conditions; the system introduces a risk taking type utility function in the economics field to quantitatively describe the fault accident result severity, thus preventing shielding phenomenon caused by using a linearity severity function, i.e., the sum of limit crossing values of a plurality of small elements is bigger than a severe element limit crossing value, thus more accurately reflecting the relative severe level.