It has been analysed systematically and in detail that how to explain three kinds of detective levels in radioactive measurements including critical "there are or not" level

detectable level and accurate detection level of radioactivity in a sample with the principle of statistics

and a group of definitions and criteria for them was proposed. The criteria are obviousely useful for making use of informations contained in an experimental data and for judging if the results of detection are effective or not. At the end of this paper

an example was given to show the application of the criteria.