A proposal for the multiclad MII optical fiber structure with ultralarge effective area and small bending loss is presented. For the proposed structure small dispersion and dispersion slope are obtained thanks to what we believe to be a novel design method. The suggested design method is based on a weighted fitness function, which is applied to the genetic algorithm optimization technique. In the meantime, the foregoing structure introduces a special fiber whose mode field diameter is small and approximately insensitive to the variation of the effective area. Compared to the work reported previously, our method can precisely set the zero dispersion wavelength. The designed dispersion-shifted single-mode fibers have effective area, mode field diameter, and quality factor respectively within [150-194.79] microm(2), [6.82-7.95] microm, and [3.04-3.85] at lambda(0)=1.55 microm. An analytical method is used for the calculation of the dispersion and its slope. These calculations give dispersion and dispersion slope of [(-2.57 x 10(-4))-(-0.085)] ps/km/nm and approximately 0.064 ps/km x nm(2), respectively.