In order to evaluate the influence of transition on the vortex structure of delta wing, a numerical simulation of VFE-2 rounded leading edge delta wing was carried out by using a high-order scheme-weighted compact nonlinear scheme and the γ－Re_θ transition model. A comparisons between calculated results and experiment data indicate that the leading edge vortex begins at a certain distance of the wing apex and the transition has great influence on the onset of leading edge vortex. Using turbulence model without transition, the leading edge separation is delayed much, while with transition model the calculated results show a good agreement with experiment data. With transition model, numerical simulation on VFE-2 rounded leading edge delta wing at variation of the angle-of-attack was carried out. The calculated results which agree well with experiment data show that at a low angle-of-attack, there is no separation-induced leading-edge vortex, but with the increase of angle-of-attack the leading edge separation displays being closer to the trailing edge and moves upstream.