There exist a lot of randomness test methods, and most of them have parameters. As it is not practical to do all randomness tests in practice, it is important to study the relations among these methods. In this paper, four kinds of relations between randomness tests and a conception of “correlation degree of randomness tests” are defined firstly based on the statistics theory firstly. And the correlation degree is measured by means of the entropy method. Then, the relevancies between the four relations and the correlation degree are proved. And an algorithm of calculating correlation degree and a selection policy are provided as well. The work of this paper is helpful for selecting reasonable and scientific randomness tests and parameters. In addition, the randomness test methods adopted by NIST (National Institute of Standards and Technology) in AES (advanced encryption tandard) are explored by using the correlation degree and some dependence relations are found.