Styrene-acrylic emulsion was synthesized by pre-emulsification and semi-continuous emulsion polymerization, with styrene and butyl acrylate as monomers. The effects of initiator dosage and ratio of polymer to cement on durability of polymeric sulphoaluminate cement were investigated. SEM, pore structure and resistance to sulfate attack were also studied. The results show that the total porosity of the polymer sulphoaluminate hardened cement paste is lowest when P/C is 7.5%. Innocuous pores of the hardened paste are the least when P/C is 5.0%. It shows that polymer particles can spread around the cement paste, and polymer particles, aggregates, hydration products and pores come into being a compact mass. Flexural strength is higher when initiator dosage is 5‰ than that is 4‰. Flexural strength is the highest when initiator dosage is 5‰ and P/C is 7.5%, in other words, the performance of resistance to sulfate attack is best when initiator dosage is 5‰ and P/C is 7.5%.