The hyperspherical harmonics expansion method is applied to a three-body model of two-neutron halo nuclei. Convergence of the expansion has been ensured. A short-range repulsive part is incorporated in the interaction between the core and the extra-core neutron, to simulate the Pauli principle. Two neutron separation energy, rms radii, correlation factor and halo neutron density distributions have been calculated for 11Li. It is found that the convergence of the two-neutron separation energy is relatively slow, while other quantities reach convergence quickly.