The distribution of strain energy and the strain relaxation degree as functions of the aspect ratio in different-shaped quantum dots were studied using finite element method. The impact on strain relaxation, originating from the shape and the inter-island distance, was also quantitatively analyzed. The results indicate that when ignoring the surface energy, the relaxation degree increases with the increase of the aspect ratio regardless of the shape, among which the truncated pyramid quantum dots tend to become steady earlier than others. With the increase of the inter-island distance, the strain energy in the dots decreases, especially in the cubic dots. A good reference is provided by the relaxation degree for controlling the shape of quantum dots.