The invention discloses a national, grid and provincial dispatching cooperative reactive backup calculation method for an ultra-high-voltage direct-current near-region power grid. The cooperative reactive backup calculation method comprises the following steps that: a national dispatching part works out convertor station alternating current bus voltage safety upper and lower limit values and reactive backup capacity demand in a rolling manner, and issues the calculation result to a grid dispatching part; a provincial dispatching part adopts a sensitivity evaluation method to convert effectivereactive backup capacity of the direct-current near-region power grid into a transformer medium voltage side of a transformer substation in a grid-provincial dispatching junction, and transmits the converted reactive backup capacity to the grid dispatching part; and the grid dispatching part cooperatively works out a grid dispatching reactive backup expected target and a provincial dispatching reactive backup expected target according to the convertor station alternating current bus voltage safety upper and lower limit values and reactive backup capacity demand issued by the national dispatching part, and the reactive backup capacity from the provincial dispatching part. By adoption of the method, through the reactive backup capacity of the ultra-high-voltage direct-current near-region power grid, influence of abnormality and a fault condition of an alternating current direct current hybrid power system to the ultra-high-voltage near-region power grid is lowered, and safe and stable operation capability of the alternating current direct current hybrid power system is improved.