The invention discloses an evaluation method for smog degree of trans-regional power network, a dispatching method and system for power grid combined anti-haze. The assessment method includes: haze data of multiple provinces is collected, including daily maximum haze concentration with time correspondence relationship of each province, total number of environmental monitoring stations along transmission lines in the province and number of environmental monitoring stations along transmission lines with mild or above level haze detected each day; according to the smog data of several provinces,the correlation coefficients of the maximum smog concentration of the first province and the second province, and the correlation coefficients of the smog area along the transmission lines of the first province and the second province are calculated; the correlation coefficients of the maximum smog concentration of the first province and the second province are calculated; according to the obtained two correlation coefficients, the intensity intervals of the smog level in the trans-regional power grid are divided. The invention can quickly and conveniently recognize the correlation between thesmog degree of two areas, and improves the pertinence and flexibility of the smog prevention and control work of the transmission line.