In recent years, the mature 3D printing technology has brought the distance between model design and product manufacturing closer. However, the high material cost is still an important factor restricting its development. Therefore, how to optimize the model structure without changing the appearance of the model, so as to reduce the printing volume of the model and cut down the printing cost is an urgent problem to be solved. For this problem, we propose a shell model construction and optimization algorithm based on stress distribution. This algorithm first constructs a distance field based on the voxel representation of the model and extracts the initial uniform thickness shell model. Then, this algorithm expands the inner surface outward adaptively, based on the von Mises stress value. The algorithm stops when the preset constraints are reached. The final optimization model is enclosed by the new inner surface and the original outer surface. Experimental results show that, the optimized shell model volume is 17.2%~24.4% of the input model volume while satisfying the constraints of appearance and mechanical stability, which reduces the printing volume greatly and lower the printing cost effectively.