A simple low temperature surface passivation method based on high pressure O2 thermal oxidation was proposed for black silicon solar cells. With this method, the nanowire textured surface of the black silicon solar cells can be effectively passivated at an extremely low temperature of ∼450 ◦ C, and a better performance was achieved compared with that treated with the conventional high temperature surface passivation. The corresponding mechanism was discussed based on current-voltage characteristics and external quantum efficiency measurements. Results demonstrate that the adverse effects associated with high temperature surface passivation can be effectively suppressed by this low temperature surface passivation process.