Based on scale space theory, two methods for muti-thresholding are put forth in this paper. One of them consists of three main steps: first, the scale space representations are derived from finer level to coarser level; then, the locations of structures are corrected from coarser level to finer level; finally, the thresholds are derived from the lifetime of structures. The other method finds the structures at a coarser scale, and then focus on finest scale step by step to derive the thresholds. Experiments show that new ways are effective and robust.