This paper is concerned about the synthesis of shape memory styrene copolymer and the investigation of the influence of cross-linking degree on its shape memory effect. The influence of cross-linking degree on shape memory effect of styrene copolymer was investigated through altering the dosage of cross-linking agent. The Tg increased from 65 to 80.7 with the gel content increase from 35% to 80% which is achieved by increasing the dosage of cross-linking agent from 1% to 4%. Moreover, the SMP experienced good SME and the largest reversible strain of the SMP reached as high as 150%. When the copolymer was heated above Tg+30 (different copolymers performed different Tg), the shape recovery speed of the copolymers increased with the gel content increase.