Impacts of acid and alkali addition on phosphorus release from sewage sludge were investigated in a microwave reactor at atmospheric pressure. Results showed that in the microwave irradiation process, though NaOH pretreatment increased the release efficiency of phosphorus from 28.8% to 59.1%, large amounts of carbon and nitrogen were correspondingly released into the supernatant. Compared to the alkali pretreatment, pretreatment of H2SO4 not only resulted in the higher release efficiency of phosphorus by 3 times (up to 84.5%), but also sharply reduced the amount of carbon and nitrogen released into the supernatant. These results suggest that H2SO4 pretreatment of sewage sludge can selectively release carbon, nitrogen and phosphorus, which is more suitable for phosphorus recovery from sewage sludge. Meanwhile, the pH range of 2.1-2.2 was optimal for phosphorus release from sewage sludge in the microwave treatment process.