By means of the weakly guiding approximation, the mode spot sizes Wx and Wy of the fundamental mode along the semimajor (x-direction) and semiminor (y-direction) axes of the fiber core in elliptical core two-mode fiber are discussed. The variation of their ratio value Wx/Wy with the operation wavelength \lambda and the length ratio a/b between the semimajor axis and the semiminor axis of the fiber core is analyzed. Based on this analysis, the distribution figures of two-lobe interferential mode