To investigate the influence of phosphorus form and pH on phosphorus release, SMT (Standard Measurements and Testing) method was applied to analyze the phosphorus chemical form in sewage sludge from different wastewater treatment plants. The release behavior of phosphorus from sewage sludge under seawater with different pH values was also investigated in lab. The results showed that: total phosphorus (TP) content of these sludge samples varied. The percentage of organic phosphorus(OP) was low, while the inorganic phosphorus (IP), accounting for 64.42% to 83.01%,was the predominant fraction of total phosphorus(TP).And the most abundant portion of inorganic phosphorus in these samples was the non-apatite inorganic phosphorus (NAIP) fraction. We have found from experiments that the phosphorus in sludge could release under acidic, neutral and alkaline conditions. Compared with neutral condition, acidic and alkaline conditions were more favorable to the release of phosphorus. The distribution of phosphorus chemical forms influenced phosphorus releasing, but does not depend on the content of total phosphorus and inorganic phosphorus simply.