Two ［P^O］ ligands, 2 ［bis(phenyl)phosphino］benzenesulphonicacid (L1) and 2 ［bis(5 methylphenyl)phosphino］benzenesulphonicacid (L2), were prepared and characterized by 1H NMR, 31P NMR, IR and MS. Catalytic systems formed by ligands and Pd(OAc)2 in situ were applied to the polymerization and copolymerization of ethylene and methyl acrylate (MA). The polymerization can be initiated without any co catalyst. The effects of reaction conditions on polymerization were investigated by L1/Pd(OAc)2. For ethylene polymerization, the mixture of ligand and Pd(OAc)2 with a mole ratio of 1∶1 provided higher catalytic activity than that with a mole ratio of 2∶1, while it is in contrast for MA polymerization, For the copolymerization, it is better with the mole ratio of 1∶1, L2/Pd(OAc)2 displayed higher catalytic activity than L1/Pd(OAc)2.