The volcanic cinder has the characteristics of irregular shape and sharper angles，and its shape characteristics affect the material engineering properties. In order to explore the shape of volcanic cinder particles，the image and shape index of volcanic cinder were obtained by AIMS aggregate image measurement system. The fractal dimension and normal distribution method were used to discuss the influence of fractal dimension and shape as the particle size change on the particle shape and fractural dimension. The differences in shape between the volcanic cinder and general rock mass were also investigated. The results show that as the particle size decreases，the elongation and texture decrease，the angularity，sphericity and fractal dimension increase，the volcanic cinder approaches spherical and massive，and the surface angularity is reduced. All the shape indicators have a good correlation，and the angularity is the most sensitive to the change of the particle size. Thus，it can be preferentially selected to describe the shape of the volcanic cinder. In addition，comparison with pebbles and crushed stone shows that the change of volcanic cinder elongation and texture is not as significant as that of the pebbles and crushed stone under different particle size. Moreover，the texture and angularity of volcanic cinder are larger than those of pebbles and crushed stone，indicating that the volcanic cinder has more angular edges and a rougher surface.