The nanoscale phthalocyanine blue dispersion was prepared by emulsion polymerization. The effect of the co-monomer structure, amount of initiator, reaction temperature and time on particle size was investigated. The results showed that styrene was suitable for preparation of encapsulated pigment dispersion, the optimal encapsulation conditions were that the weight ratio of styrene to phthalocyanine blue, initiator APS to St, reaction temperature and reaction time was about 20% , 1.0%, 70~80℃ and 2h respectively. The thermal stability, pH stability and centrifugal stability were improved greatly after emulsion polymerization, FT-IR and TEM showed that some copolymer was coated on the phthalocyanine blue pigment surface, particle size distribution measured by DLS showed that the particle size of encapsulated pigment dispersion was small and uniform.