Abstract: The cross section is measured of e+e-→π+π- in the energy range between 600 and 900 MeV/c2 with a 2.93 fb-1 data set taken at the center-of-mass energy 3773 GeV at BESIII. The initial state radiation technique is used, and the total systematic uncertainty is estimated to be 09%. The squared form factor |Fπ|2 is extracted, and comparisons are made with results from both KLOE and BaBar. The two-pion contribution to the hadronic vacuum polarization contribution to (g-2)μ is calculated to be aππ,LOμ(600~900 MeV/c2)=(3682±25stat±33sys)×10-10.