We are developing a cylindrical GEM detector with analog readout to upgrade the Inner Tracker of the BESIII experiment at IHEP (Beijing). The new detector will match the requirements for momentum resolution (σpt /pt ∼ 0.5% at1 GeV) and radial resolution (σxy ∼ 100 μm) of the existing drift chamber and will improve significantly the spatial resolution along the beam direction (σz ∼ 150 μm) with very small material budget (about 1% of X 0). A beam test has been performed at CERN in order to measure the performance of a BESIII GEM prototype in a magnetic field up to 1 tesla. An overview of the project and the preliminary results of the test will be presented in the talk. The project has been recognised as a Significant Research Project within the Executive Programme for Scientific and Technological Cooperation between Italy and PRC for the years 2013-2015, and more recently has been selected as one of the project funded by the European Commission within the call H2020-MSCA-RISE-2014.