The invention discloses a method for improving the qualified rate of ultra-thick plate flaw detection. The method comprises the following steps of LF refining, VD vacuum treatment, continuous castingand rolling, wherein the VD vacuum treatment process and the vacuum degree are 40-67 Pa, the vacuum maintaining time is 15-18 minutes, the argon is stirred for 12-15 minutes in a vacuum maintaining process, and the argon is subjected to soft blowing for 7-10 min. According to the method, gas in molten steel is fully released through the soft blowing after the large argon stirring and the VD breaking in the VD vacuum treatment process, and impurities in the molten steel are fully floated, so that the hydrogen and the inclusions in the molten steel are greatly reduced, and the flaw detection qualified rate of an ultra-thick plate is effectively improved; and the ultra-thick plate flaw detection is combined with GB. The qualified rate of the flaw detection is greater than or equal to 98%; andthe content of the ultra-thick plate is in a range from 0.7-1.0 ppm, and the content of the inclusion is in a range of 0.5-1.0.