This study systematically investigated the Lean Blowoff (LBO) limits of Two-Dimensional (2D) bluff-body stabilized premixed flames by varying the air mass flow rate, inflow temperature, bluff-body width, and fuel type. The data of LBO limits were analyzed and fitted according to the Damköhler (Da) and Reynolds (Re) numbers, and the fitting accuracy of LBO data was highly improved by a modified characteristic length simultaneously considering the length and width of the bluff body, which is usually neglected in the previous studies. Moreover, to our knowledge, this is the first time that simultaneous transverse and spanwise OH*-Chemiluminescence (CL) imaging has been performed to examine the three-dimensional behavior of the LBO process. The flame stability is heavily affected by the mass and energy transport between reactants and products in both directions, potentially leading to the flame pinch-off. The intensity and position of the upstream flame after pinch-off are decisive to the occurrence of the following LBO. When the upstream flame after pinch-off is weak and close to the bluff body, it cannot re-ignite the downstream unburnt gas. Subsequently, a permanent downstream extinction occurs, and the LBO takes place. The results help understand the LBO mechanism of 2D bluff-body stabilized flames.