Abstract: In this paper, the sectional optimization with the lightestweight of the shell structure as the objective function is carried outby using two level optimization methods based on discrete variables and the style ofbar group and the effect of different mesh densities on optimal results are mainlyconsidered. In the course of the optimization procedure, integral stabilityconstraints are shown to be good for practical engineering.For K6 type of single-layer shell structure with span of 50\,m and rise-spanratio of 1/5, 42 shell models with six different bar groups and sevendifferent mesh densities were built and optimized. Finally, an new and betterchoice of bar group and mesh density is obtained.