The invention discloses a calibration method for detection efficiency of a radioactivity iodine active carbon sampling filter box. The calibration method for detection efficiency of the radioactivity iodine active carbon sampling filter box comprises steps of using a standard plane source calibration detection device to detect various depths of a sampling filter box according to an adsorption rule of the iodine in the sampling filter box, and obtaining detection efficiency of a detector on iodine absorbed on the sampled filter box through measuring the sampling filter box by placing the sampling filter box forward and reversely for once. The calibration method for detection efficiency of the radioactivity iodine active carbon sampling filter box provides technology supports to accurately and reliably measuring a radioactivity iodine concentration in places, like a nuclear power station, which relates to gaseous state radioactivity iodine monitoring. The calibration method of the invention uses a changing curve which is measured by laboratory calibration and shows that the plane source detection efficiency changes along the depth of the plane source in the sampling filterbox and full-energy peak counting of the detection device which is detected when the filter box is respectively placed forward and reversely according to the experiment. The calibration method for detection efficiency of the radioactivity iodine active carbon sampling filter box is simple, can fast obtain an index progressive decrease distribution parameter of the iodine in the sampling filter box and detection efficiency of the detector on the iodine, and the calibration method can be traced back to a national metering standard.