Abstract: A new background reconstruction algorithm is proposed to overcome the problems in the current algorithms，which is based on sub-blocks and employs symmetrical differencing.First，the original symmetrical differencing is improved.Then，background is reconstructed based on the symmetrical differencing results.This algorithm makes use of the spatial information in part，only need simple computation，and need not store history images.Moreover，it can self-adapt to the changes of illumination and of background.Experimental results indicate the fast and efficient performance of the algorithm in background reconstruction.