Calculation of the equipment failure rate is a key to the assessment of power system operation risk .The method of equipment fault rate based on the condition maintenance rate algorithm is applied to the assessment of power system operation risk.It also improves the accuracy and reliability of equipment failure rate in a certain extent. The power system operation risk assessment methods based on the condition maintenance take full consideration of the existing uncertainty in power grid operation .It describes the running risk level of the power grid comprehensively through the five risk index which contains the line overload, transformer overload, over voltage, low voltage and loss of load , and the layer analysis method are applied to the calculation of the comprehensive risk index of power network, which provides a reference norm to the comparison of risk under different operating modes of power grid . Through the practical example analysis, this paper demonstrates the effectiveness of the power system operation risk assessment method based on condition maintenance.