Autocorrelation test was a statistical test to evaluate the correlation between one sequence and the corresponding non-cyclic left-shifted d bits sequence.It was impractical to adopt all the values of d since its range was often very wide.Three relations between parameters of randomness test were defined firstly.Then the relationships among the subclass D={1

2

m/4

m/2

3m/4

m

2m}of autocorrelation test for block cipher were studied by statistical experiments

where m was block length.The experiments show that the prefer choice of parameter d is m when doing autocorrelation test for block cipher.The method is also available for parameter selection of other randomness test for other types of cryptosystem.