The invention relates to a cross-region power networking complementarity judging method and device. The method comprises steps: according to the average load demand of each to-be-networked region, theaverage wind power output of each to-be-networked region and the average photovoltaic output of each to-be-networked region, the net load average power of each to-be-networked region is determined; according to the net load average power of each to-be-networked region, the peak-to-valley difference of the net load average power of each to-be-networked region is determined; according to the peak-to-valley difference of the net load average power of each to-be-networked region, a power interconnection complementarity coefficient between the to-be-networked regions is determined; and according to the power interconnection complementarity coefficient between the to-be-networked regions, the networking complementarity between the to-be-networked regions is judged. According to the technical scheme provided in the invention, the fluctuating factors such as the new energy output and the load demand can be comprehensively considered, cross-region power networking complementarity is fully reflected, and the value generated for power system peak shaving by the cross-region power networking can be accurately characterized.