With the rapid development and extensive applications of computer technology, network technology, communication technology, and Internet in particular, the security of network information is becoming increasingly key problem that must be solved urgently. That applying chaos theory to secure communication and information encryption has already become one of the hot research projects on the combination of nonlinear science and information science, and it is a novel branch of high-tech research fields. In this paper ， a chaotic encryption algorithm based on skew tent map is proposed. In the process of encryption, it updates look-up table depends on plaintext and external key, the 8-bit subkey is dynamically generated with skew tent map depended on updating look-up table，the key is initial condition of skew tent map, control parameter p and a external key K. Theoretical analysis and simulated experiments show that the algorithm can resist the statistic and differential attacks, and the algorithm have high security.