In this study modified starch were used as anti-washout promoters of injectable calcium phosphate cement (CPC) and the effects of the modified starch on the injectability, anti-washout performance, setting time, compressive strength, phase evolution and microstructure of this cement were investigated. The injectability of the cement was improved by adding the modified starch (0.5-2.0%). After mixing with modified starch (0.5-2.0%), the cement showed better anti-washout performance than that without modified starch after immersed and shaken in SBF. Especially, when the content of the modified starch was 1.0%, the remaining percentage of the cement was reached to 92.6%, but only 5.9% of the CPC paste remained and set for the sample without modified starch after shaken for 2 hrs. The compressive strength of cements significantly increased from 44 MPa to 54 MPa when 0.5% of modified starch was added. And a slight increase on the mechanical strength can be observed for other concentrations. Powder X-ray diffraction analysis revealed no significant difference for the conversion of the cement to hydroxyapatite for any concentrations of modified starches. The influence of the modified starch on the microstructure of the set cement was also studied. The results showed the modified starch would reduce the acicular crystal size of hydroxyapatite accompanied with little flaky crystals generation and made a compact structure. It is concluded that modified starch, a suitable anti-washout promoter, improved the performance of CPC.