Based on the vector-ray tracing (VRT) model, the optical caustic structures of homogeneous ellipsoid droplets in the third-order and fourth-order rainbow regions are studied. The evolution process of the optical caustic structure is investigated in detail. The simulated result and fringe curvature of the third-order rainbow fringe as well as the relationship between the cusp location of the third-order rainbow and hyperbolic umbilic fringes and the aspect ratio are obtained.