The invention provides a half sub region relevant optical measurement method of a strain field in a strain localization zone. An image of one surface of an object in a loaded process is collected; the displacement and the strain of each measuring point on the image and the inclination angle of the strain localization zone to be measured are obtained; two parallel measuring lines are arranged in the normal direction of the strain localization zone to be measured; a plurality of measuring points are arranged; the coordinates and the displacement of the measuring points simultaneously positioned on the measuring line and the starting boundary line of the strain localization zone to be measured are obtained; the coordinates and the displacement of the measuring points with the distance being a half of the distance of the measuring lines are determined inside and outside the strain localization zone to be measured; the strain of a rectangular pixel block is calculated; the distribution rule of the strain field inside the strain localization zone to be measured is obtained. The time-space distribution rule of the strain field in the strain localization zone can be better measured; the strain distribution in the strain localization zone obtained through measurement is smooth, continuous and accurate; the measurement precision of the inside strain field in the strain localization zone is improved; the wide application is realized in the field of solid experimental mechanics.