Abstract: The relationships between factors in signal processing software is complicate, even some factors is redundant. And it's difficult to determine equivalence classes of factors. Traditional methods deal badly with test generation of signal processing software, by lager size and poor result. This paper discusses a new way of using variable strength combinatorial coverage into test generation of signal processing software. On the basis of the density algorithm, the application steps of the approach are given. Based on formalization expression of algorithm, a method is suggested to optimize coverage requirement. Experimental results show that the suggested method reduces the size of test cases, and improves the effect of test cases.