The invention discloses a large and small running mode reactive power optimizing and joint adjusting method of an electric system. The method comprises the following steps of: reading in the BPA (back propagation algorithm) data of the electric network and carrying out power flow calculation by means of a PSD-BPA (phase sensitive detection-back propagation algorithm) software tool; for electric network data, the power flow of which is not converged, adjusting through an optimal power flow module, carrying out error screening and correction on a network parameter and a running parameter, and giving out a reasonable running mode under a network area framework; obtaining the data of a needed network area from the converged electric network data through an equivalent method, and analyzing data needed by a reactive power optimizing module from the converged electric network data; and carrying out large and small running mode reactive power joint optimization. By using the method, a transformer tapping adapting to a large running mode and a small running mode can be found out; a reactive power voltage optimization configuration policy is given out; the reactive power voltage optimization running between each two voltage classes is realized; the voltage percent of pass of the whole network is improved; a theoretical basis is provided for making the running modes of the electric network; and the electric network is guaranteed to run safely and stably.