The invention discloses a device and a method for evaluating the repairing capability of a well cementation set cement exogenous self-repairing material. The device is composed of a nitrogen cylinder,a gas cylinder containing a repairing medium, a kettle body, a high-pressure pump, an outer pressure pump, a peripheral pressure sensor, an inner peripheral pressure sensor, a temperature regulator,an inner galvanic couple, an outer galvanic couple and a computer, a simulated rock core, a cement sheath and a simulated sleeve are arranged in the kettle body, three gas inlets are formed in a kettle cover, and three gas outlets are formed in the kettle bottom. The method comprises the following steps: placing the simulated rock core and the simulated sleeve in the kettle body, injecting cementpaste into an annular space, and curing to form the cement sheath; setting the temperature according to the actual working condition of the well bottom; injecting nitrogen into the simulated sleeve until the cement sheath generates cracks; setting inner peripheral pressure and outer peripheral pressure according to underground working conditions; introducing gas containing a repair medium into thecement sheath; and judging the self-repairing capability of the set cement according to the difference value of the accumulated flow of the introduced gas and the discharged gas. According to the invention, the self-repairing capability of the cement sheath can be evaluated under different pressures and temperatures.