Confinement loss for the fundamental mode in the triangular lattice microstructured optical fibers with elliptical air holes is analyzed using the complex finite element method under the perfectly matched layer boundary condition. It is shown by the numerical results that the confinement losses decrease when the pitch of the air holes, the air-filling fraction and the rings of the air holes increase. In addition, the confinement losses are dependent on the fundamental mode polarization, and the confinement loss ratio of the y-polarized mode compared to the x-polarized mode increases with increasing pitch of the air holes, the air-filling fraction and the hole ellipticity. In the end, two kinds of highly nonlinear microstructured optical fibers that can achieve single-polarization, single mode transmission are designed.