In order to improve communication security, proposed a chaotic block cryptographic scheme based on the coupled piecewise nonlinear map. Using the coupled chaotic systems to generate random binary sequences, a key-dependent shift approach permuted the plain-text block and then using the classical chaotic masking technique encrypted the plain-text block. Simulation results show that the proposed algorithm has excellent cryptographic properties such as diffusion and confusion properties and it can resist the know plain-text attacks and chosen plain-text attacks.