The invention discloses a rapid reconstructing method of a compressed sensing image based on least square optimization. Optimized reconstruction is carried out to signals basing on a least square method; a parameter-whole correlation degree is measured by newly defined whole correlation; a most correlated atom aiming at an image is selected; the number of iterations is reduced; a subblock reconstruction theory is introduced; a subblock size and a measuring matrix are redesigned; the calculation scale of the reconstruction operation is reduced; the optimized reconstruction is carried out to signals basing on the least square method; the reconstructing precision and the convergence rate are ensured; the experiment result shows that the reconstructing time of the signals is remarkably reduced through the FBWRFI algorithm; the increasing trend of the reconstructing time increasing at high speed as the signals increase is changed into linearity; and the effectiveness of the algorithm is proved.