The invention discloses a well cementation cement slurry leak-proof performance evaluation device and method by simulating leakage of holes and gaps. The well cementation cement slurry leak-proof performance evaluation device is mainly composed of a base 9 provided with a bracket, a liquid quantity collecting platform 8, a heating outer cylinder 2, a temperature sensor 14, a slurry cylinder 1, a leakage medium 4, an experiment pressure switch 13, an air source 10 and a data collecting and processing system 3; and the heating outer cylinder 2 is fixed with the bracket of the base 9 provided with the bracket, the liquid quantity collecting platform 8 is stored on the base, the slurry cylinder 1 is mounted in the heating outer cylinder, the lower end of the slurry cylinder is provided with the leakage medium 4, and the leakage medium is provided with a hole channel 16 and a gap channel 17. The well cementation cement slurry leak-proof performance evaluation method comprises the steps thatan experimental temperature is set to preheat the device; the leakage medium parameter is input; cement slurry is prepared; the prefabricated cement slurry is loaded into the slurry cylinder, and thepressure is adjusted to the initial leakage pressure P1; the leakage pressure of the cement slurry is gradually increased until the final pressure-bearing value is reached; and the leak-proof abilityof the cement slurry is calculated and obtained. The well cementation cement slurry leak-proof performance evaluation device and method by simulating leakage of the holes and the gaps are easy to operate, high in comparability and wide in application scope, and have the wide market application prospects.