Pseudorandom sequence plays an important role in information hiding. But in many circumstances, what we need is pseudorandom sequence with adjustable density other than balanced pseudorandom sequence. Compared with the study on other techniques in information hiding, research on special sequence for information hiding is rare. This paper proposes the concept of density adjustable pseudorandom sequence for the first time and presents its applications. We also give a general construction method of density adjustable pseudorandom sequence generator. Theoretical analysis proves our method can generate sequence approaching to any fixed density with arbitrary precision as well as preserving excellent randomness. Furthermore, two case studies are given to demonstrate it is applicable for information hiding. The main contribution of this paper is providing the density adjustable pseudorandom sequence as a fundamental primitives of information hiding.