Five kinds of acrylic acid-co-sodium methallyl sulfonate(PC-1~5) were synthesized by free radical polymerization, and these copolymers′ influences on building gypsum system were studied, and compared with comb-like polycarboxylate-type(PC) and FDN. The results indicated that when the dosage was 0.3%: PC-4(nacrylic acid:nsodium methallyl sulfonate = 6:1) was the best copolymer on water-reducing rate, achieved 22%, and the longest slump retain，reached 70 min, and the lowest water absorption rate at 2h, achieved 16%, 11.5% lower than the blank, and the bending and compressive strength enhanced 30%, 31% respectively, and the highest softening coefficient, achieved 0.36, 0.1 higher than the blank. It was found that building gypsum hydration crystal form from needle turned to flake when added PC-4. The major functional groups of PC-4 was determined by IR. This shows that the adaptability of linear copolymer PC-4 on building gypsum system was fine.