Multi Objective Evolutionary Algorithm (MOEA) has been used to design a high safe and high efficiency cryptosystem. Because stream cipher cryptosystem makes itself can not be decrypted theoretically, a large majority of sequence cipher cryptosystem use a short key to produce a key sequence with the same period. But the key sequence produced above seldom has good randomness and is unsafe frequently. This paper proposes an improved approach Stream Cipher Generation Method based on Particle Gradient Multi-Objective Evolutionary Algorithm (PGEASCG) to produce a key sequence with good randomness and reliability. Simulation results clearly illustrate that the proposed approach is very efficient and could easily get the optimal key sequence.