The influence of V/III ratio on the formation of quantum dots (QDs) grown by metal-organic chemical vapor deposition (MOCVD) is investigated by atomic force microscopy (AFM) and photoluminescence (PL) measurements. As V/III ratio increases, the density of QDs decreases accompanied by the transition of QD size distribution from bimodal (at V/III = 9) to single-modal (at V/III = 15), and then to bimodal (at V/III = 25) again, which is attributed to the change of the indium-species migration length at different V/III ratios. There are PL spectrum redshifts and the PL peak intensity decreases as V/III ratio increases.