In this paper, we propose a novel algorithm for pseudo random number sequence generator based on the samples of Chen chaotic system. The proposed algorithm can be used to generate cryptographic keys for digital images among the cryptography applications. Moreover, our pseudo random number generator solves the problem of the non-uniform probability distribution of sequence generated directly by the Chen chaotic system. The various statistical tests such as Diehard battery test and NIST SP 800-22 randomness test verify that the sequences generated by our proposed scheme have good statistical properties. The experimental results of the security analysis validate the high capability of the proposed method to withstand various attacks.