Concentrator photovoltaic (CPV) performs high conversion efficiency, however it requires a solar tracking system which limits the installation place and ground coverage ratio of the tracker array. Microtracking CPV has a potential to solve those problems however searching a better concentrator optics and tracking mechanism is still needed. This paper examined a two-shell spherical lens concentrator for microtracking CPV by optical simulations. The result shows that two-shell spherical lens with a high refractive index (RI) outer shell and a low RI core shell exhibits higher optical efficiency and wider mechanically allowable angle, i.e., acceptance angle, than the single-shell spherical lens.