The invention relates to the field of electric power system dispatching and operation technology and discloses an electric power system spinning reserve optimization method based on curve piecewise linearization. According to the method, total cost comprising fuel cost and reliability cost is minimized to decide spinning reserve capacities of a system at all moments. The method comprises the specific steps that first, an operation optimization model without consideration of a spinning reserve demand is solved, and a basic unit combination scheme of all generator units is obtained; second, on the basis of the basic unit combination scheme obtained in the first step, a reliability curve with spinning reserves being the horizontal axis and reliability indexes being the longitudinal axis is formed according to the moments, and the reliability curve is subjected to piecewise linearization to obtain coefficients of all linear segments; and third, the reliability curve based on piecewise linearization is added into the operation optimization model in a constraint form, and calculation is performed again to obtain an electric power system spinning reserve considering system reliability.