Abstract: Concerning the storage characteristics of digital map, a chaotic sequence encryption algorithm is presented. The user’s key is first hashed as the seed of chaotic mapping by a Hash function. After several iteration steps, the chaotic sequences are mapped to ASCII codes, and using the ASCII codes to one by one XOR every byte of the map data. In order to avoiding the localization of the finite precision, we change the parameter of the chaotic mapping with step length. Comparing with DES and A5algorithms, computing results show that our algorithm is fairly good in efficiency, security and simplicity.